Doxygen: accept .dox as pure doxygen, and interpret everything as C

Doxyfile.in

@@ -316,7 +316,7 @@ OPTIMIZE_OUTPUT_SLICE  = NO
 # Note that for custom extensions you also need to set FILE_PATTERNS otherwise
 # the files are not read by doxygen.
 
-EXTENSION_MAPPING      =
+EXTENSION_MAPPING      = dox=C h=C c=C
 
 # If the MARKDOWN_SUPPORT tag is enabled then doxygen pre-processes all comments
 # according to the Markdown format, which allows for more readable
@@ -845,7 +845,8 @@ INPUT_ENCODING         = UTF-8
 # *.f, *.for, *.tcl, *.vhd, *.vhdl, *.ucf, *.qsf and *.ice.
 
 FILE_PATTERNS          = *.c \
-                         *.h
+                         *.h \
+                         *.dox
 
 # The RECURSIVE tag can be used to specify whether or not subdirectories should
 # be searched for input files as well.