Configure doxygen STRIP_FROM_INC_PATH option

so that include directives are correct in the generated documentation.

Author: kimci86

doc/doxyfile.in

@@ -199,7 +199,7 @@ STRIP_FROM_PATH        =
 # specify the list of include paths that are normally passed to the compiler
 # using the -I flag.
 
-STRIP_FROM_INC_PATH    =
+STRIP_FROM_INC_PATH    = "@DOXYGEN_INPUT_DIR@/include"
 
 # If the SHORT_NAMES tag is set to YES, doxygen will generate much shorter (but
 # less readable) file names. This can be useful is your file systems doesn't