Merge branch 'regex-pcre'

Implement wxRegEx using PCRE2.

See https://github.com/wxWidgets/wxWidgets/pull/2438

docs/changes.txt

@@ -12,7 +12,12 @@ INCOMPATIBLE CHANGES SINCE 3.0.x:
 Changes in behaviour not resulting in compilation errors
 --------------------------------------------------------
 
+- wxRegEx now uses PCRE library, changing the meaning of some exotic regular
+  expressions using wxRE_ADVANCED syntax, please see its documentation for more
+  details.
+
 - wxRibbonButtonBar::DeleteButton() now deletes and not just removes the button.
+
 - Default interpolation mode in wxGDIPlusContext under MSW is now
   wxINTERPOLATION_DEFAULT and not wxINTERPOLATION_GOOD as in 3.0 for
   consistency with OS X, call SetInterpolationQuality() explicitly if needed.

docs/doxygen/mainpages/const_cpp.h

@@ -201,7 +201,9 @@ Currently the following symbols exist:
         Defined if the current port supports radio menu items (see wxMenu::AppendRadioItem).}
 @itemdef{wxHAS_RAW_BITMAP, Defined if direct access to bitmap data using the classes in @c wx/rawbmp.h is supported.}
 @itemdef{wxHAS_RAW_KEY_CODES, Defined if raw key codes (see wxKeyEvent::GetRawKeyCode are supported.}
-@itemdef{wxHAS_REGEX_ADVANCED, Defined if advanced syntax is available in wxRegEx.}
+@itemdef{wxHAS_REGEX_ADVANCED, Defined if advanced syntax is available in
+    wxRegEx. This is always the case in wxWidgets 3.1.6 and later, so this
+    symbol doesn't need to be tested any more.}
 @itemdef{wxHAS_TASK_BAR_ICON, Defined if wxTaskBarIcon is available on the current platform.}
 @itemdef{wxHAS_WINDOW_LABEL_IN_STATIC_BOX, Defined if wxStaticBox::Create()
     overload taking @c wxWindow* instead of the text label is available on the current platform.}

docs/readme.txt

@@ -148,9 +148,8 @@ If you use JPEG image handler, documentation for your program should contain
 following sentence: "This software is based in part on the work of the
 Independent JPEG Group". See src/jpeg/README for details.
 
-If you use wxRegEx class on a system without native regular expressions support
-(i.e. MS Windows), see src/regex/COPYRIGHT file for Henry Spencer's regular
-expression library copyright.
+If you use wxRegEx class, please see 3rdparty/pcre/LICENCE for PCRE licence
+details.
 
 If you use wxXML classes or XRC, see src/expat/COPYING for licence details.