Doxygen: Fix skipping extension-less C++ #include files

Careful, not to include `Doxyfile` and ``LICENSE` extension-less files
from repository root.

Signed-off-by: Simon Rozman <simon@rozman.si>

Doxyfile

@@ -310,7 +310,7 @@ OPTIMIZE_OUTPUT_SLICE  = NO
 #
 # Note see also the list of default file extension mappings.
 
-EXTENSION_MAPPING      =
+EXTENSION_MAPPING      = no_extension=C++
 
 # If the MARKDOWN_SUPPORT tag is enabled then doxygen pre-processes all comments
 # according to the Markdown format, which allows for more readable
@@ -864,7 +864,7 @@ WARN_LOGFILE           =
 # spaces. See also FILE_PATTERNS and EXTENSION_MAPPING
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  =
+INPUT                  = include/stdex
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses
@@ -893,7 +893,7 @@ INPUT_ENCODING         = UTF-8
 # comment), *.py, *.pyw, *.f90, *.f95, *.f03, *.f08, *.f18, *.f, *.for, *.vhd,
 # *.vhdl, *.ucf, *.qsf and *.ice.
 
-FILE_PATTERNS          =
+FILE_PATTERNS          = *
 
 # The RECURSIVE tag can be used to specify whether or not subdirectories should
 # be searched for input files as well.