python_rank_filter.cxx -> rank_filter_py.cxx: Renamed to rank_filter_py.
CMakeLists.txt: Updated to reflect the name change.
rank_filter.hxx -> include/rank_filter.hxx: Moved to include.
rank_filter.hxx -> include/rank_filter.hxx: Moved to src.
test_rank_filter.cxx -> test/test_rank_filter.cxx: Moved to test.
CMakeLists.txt: Add the include directory to our list of paths.
CMakeLists.txt: Change path to src for building.