Fix unknown command warning in generating doxygen

Fix unknown command warning in generating doxygen

elementary/src/lib/elm_access.h:238: warning: Found unknown command `\type'
elementary/src/lib/elm_bg_legacy.h:98: warning: Found unknown command `\r'
elementary/src/lib/elm_bg_legacy.h:98: warning: Found unknown command `\g'
elementary/src/lib/elm_object.h:124: warning: Found unknown command `\content'
elementary/src/lib/elm_image_legacy.h:82: warning: Found unknown command `\group'
elementary/src/lib/elm_image_legacy.h:56: warning: Found unknown command `\group'