Add .gitignore for CMake generated Doxygen files.
Add .gitignore for CMake generated Doxygen files.

dbaarda/librsync,sourcefrog/librsync,dbaarda/librsync,dbaarda/librsync,librsync/librsync,sourcefrog/librsync,sourcefrog/librsync,sourcefrog/librsync,librsync/librsync,librsync/librsync,dbaarda/librsync,librsync/librsync