Ultrastarparser

Various stuff

- Big improvements to the readme
- ability to export library as json or csv
- ability to validate karaoke

Lots of internal refactoring here. Also tons of bugfixes, vastly improved docstrings and new methods for both files and libraries.

Lots of bugfixes, and improvements to docstrings. No breaking changes.

Features:
- add() and remove() for library
- is_duet() and validation functions for ultrastarfile
- additional optional arguments for functions like reorder_auto() to allow for custom reordering.

Bugfix for automatic reordering of tags.

Fix for bom characters in text file.