Escape double dashes in Doxygen input to preserve them

By default double dashes are converted to en-dashes in the output (and triple
ones -- to em-dashes), but this is undesirable when double dashes are used not
as a punctuation mark but in command line options or as C++ decrement
operator, so escape them to avoid such conversion in this case.

docs/doxygen/overviews/backwardcompatibility.h

@@ -87,7 +87,7 @@ next earlier stable branch the default is 0, so @c WXWIN_COMPATIBILITY_2_4 = 0
 for 2.8.x. Earlier than that, obsolete features are removed.
 
 These macros can be changed in @c setup.h. Or on UNIX-like systems you can set
-them using the @c --disable-compat26 and @c --enable-compat24 options to
+them using the @c \--disable-compat26 and @c \--enable-compat24 options to
 configure.
 
 They can be useful in two ways:

docs/doxygen/overviews/container.h

@@ -96,8 +96,8 @@ uses its knowledge about wxString reference counting schema.
 
 To build wxWidgets with the standard containers you need to set
 wxUSE_STD_CONTAINERS option to 1 in @c wx/msw/setup.h for wxMSW builds or
-specify @c --enable-std_containers option to configure (which is also
-implicitly enabled by @c --enable-stl option) in Unix builds.
+specify @c \--enable-std_containers option to configure (which is also
+implicitly enabled by @c \--enable-stl option) in Unix builds.
 
 The standard container build is mostly, but not quite, compatible with the
 default one. Here are the most important differences:

docs/doxygen/overviews/envvars.h

@@ -22,7 +22,7 @@ wxWidgets programs.
         (Unix only.)
         Overrides installation prefix. Normally, the prefix
         is hard-coded and is the same as the value passed to @c configure via
-        the @c --prefix switch when compiling the library (typically
+        the @c \--prefix switch when compiling the library (typically
         @c /usr/local or @c /usr). You can set WXPREFIX if you are for example
         distributing a binary version of an application and you don't know in advance
         where it will be installed.}

docs/doxygen/overviews/exceptions.h

@@ -114,10 +114,10 @@ documentation of these functions for more details.
 To use any kind of exception support in the library you need to build it
 with @c wxUSE_EXCEPTIONS set to 1. It is turned on by default but you may
 wish to check @c include/wx/msw/setup.h file under Windows or run @c configure
-with explicit @c --enable-exceptions argument under Unix.
+with explicit @c \--enable-exceptions argument under Unix.
 
 On the other hand, if you do not plan to use exceptions, setting this
-flag to 0 or using @c --disable-exceptions could result in a leaner and
+flag to 0 or using @c \--disable-exceptions could result in a leaner and
 slightly faster library.
 
 As for any other library feature, there is a sample (@c except)

docs/doxygen/overviews/nonenglish.h

@@ -108,7 +108,7 @@ catalog, you may configure wxWidgets to use non-English msgids and translate to
 English using message catalogs:
 
 @li If you use the program @c xgettext to extract the strings from the source
-    code, specify the option <tt>--from-code=@<source code charset@></tt>.
+    code, specify the option <tt>\--from-code=@<source code charset@></tt>.
 @li Specify the source code language and charset as arguments to
     wxLocale::AddCatalog. For example:
     @code

docs/doxygen/overviews/unicode.h

@@ -184,7 +184,7 @@ under all systems. Thus, under Microsoft Windows, UCS-2 (simplified version of
 UTF-16 without support for surrogate characters) is used as @c wchar_t is 2
 bytes on this platform. Under Unix systems, including OS X, UCS-4 (also
 known as UTF-32) is used by default, however it is also possible to build
-wxWidgets to use UTF-8 internally by passing @c --enable-utf8 option to
+wxWidgets to use UTF-8 internally by passing @c \--enable-utf8 option to
 configure.
 
 The interface provided by wxString is the same independently of the format used
@@ -208,7 +208,7 @@ of conversions (and also reduced memory usage of UTF-8 compared to UTF-32 for
 the European languages) can be important. If the environment in which your
 program is running is under your control -- as is quite often the case in such
 scenarios -- consider ensuring that the system always uses UTF-8 locale and
-use @c --enable-utf8only configure option to disable support for the other
+use @c \--enable-utf8only configure option to disable support for the other
 locales and consider all strings to be in UTF-8. This further reduces the code
 size and removes the need for conversions in more cases.
 
@@ -216,7 +216,7 @@ size and removes the need for conversions in more cases.
 @subsection overview_unicode_settings Unicode Related Preprocessor Symbols
 
 @c wxUSE_UNICODE is defined as 1 now to indicate Unicode support. It can be
-explicitly set to 0 in @c setup.h under MSW or you can use @c --disable-unicode
+explicitly set to 0 in @c setup.h under MSW or you can use @c \--disable-unicode
 under Unix but doing this is strongly discouraged. By default, @c
 wxUSE_UNICODE_WCHAR is also defined as 1, however in UTF-8 build (described in
 the previous section), it is set to 0 and @c wxUSE_UNICODE_UTF8, which is

docs/doxygen/overviews/unixprinting.h

@@ -20,7 +20,7 @@ using PostScript which never really matched the screen display.
 
 Since GTK+ 2.10, support for printing has been added to GTK+ itself and
 beginning with wxWidgets 2.9, GTK+ printing is used by default (i.e. unless
-<tt>--without-gtkprint</tt> was explicitly used when configuring the library).
+<tt>\--without-gtkprint</tt> was explicitly used when configuring the library).
 Support for GTK+ print is detected dynamically, i.e. during the run-time: if it
 is found, printing will be done through GTK+, otherwise the application will
 fall back to the old PostScript printing code. This allows the applications

docs/doxygen/overviews/xrc.h

@@ -255,19 +255,19 @@ To compile binary resource files, use the command-line @c wxrc utility. It
 takes one or more file parameters (the input XRC files) and the following
 switches and options:
 
-@li -h (--help): Show a help message.
-@li -v (--verbose): Show verbose logging information.
-@li -c (--cpp-code): Write C++ source rather than a XRS file.
-@li -e (--extra-cpp-code): If used together with -c, generates C++ header file
+@li -h (\--help): Show a help message.
+@li -v (\--verbose): Show verbose logging information.
+@li -c (\--cpp-code): Write C++ source rather than a XRS file.
+@li -e (\--extra-cpp-code): If used together with -c, generates C++ header file
     containing class definitions for the windows defined by the XRC file (see
     special subsection).
-@li -u (--uncompressed): Do not compress XML files (C++ only).
-@li -g (--gettext): Output underscore-wrapped strings that poEdit or gettext
+@li -u (\--uncompressed): Do not compress XML files (C++ only).
+@li -g (\--gettext): Output underscore-wrapped strings that poEdit or gettext
     can scan. Outputs to stdout, or a file if -o is used.
-@li -n (--function) @<name@>: Specify C++ function name (use with -c).
-@li -o (--output) @<filename@>: Specify the output file, such as resource.xrs
+@li -n (\--function) @<name@>: Specify C++ function name (use with -c).
+@li -o (\--output) @<filename@>: Specify the output file, such as resource.xrs
     or resource.cpp.
-@li -l (--list-of-handlers) @<filename@>: Output a list of necessary handlers
+@li -l (\--list-of-handlers) @<filename@>: Output a list of necessary handlers
     to this file.
 
 For example: