Change filenames to use fs::path and absolute paths instead of relative to song folder. Remove useless copypasta from song parsers. Incomplete work, has bugs.
Avoid re-processing of header fields in songparser-sm too, alike the earlier change in songparser-txt.
Use absolute paths in songparser-sm.
Greatly improved media file autodetection. Now also detects audio files.
Cleanup and fix FoF format support.
Do not display current value of sort in parenthesis after sort order text (it won't fit on screen). We can implement a better UI for displaying this data if desired.
Do not render black box in jukebox mode while cover is still being loaded. Use song bg as fallback in cover browser if no cover is available.
Use absolute paths in songparser-ini too.
Cleanup.
Merge branch 'master' into fspath

Conflicts:
	game/songs.cc
Continued fs::path cleanup. Trying to fix compatibility problems on Windows. Other cleanup...

- PNG loading FILE* I/O replaced by std::fstream and memory buffer
- Added image.cc and util.cc to cut down compile times (remember to re-run CMake)
Minor cleanup.
Merge branch 'master' into fspath
Merge branch 'master' into fspath
Tell the name of the song file when reporting parsing warning...
Fix compilation on MinGW.
Merge branch 'fspath'