:rocket: Added
- Write modes (`w`, `x`, `r+`, `w+`, `x+`) :tada:
- Allow to `seek` past the end of the fileobj
- Calling `len` on a fileobj gives its length, and `bool` tells if it is empty
- Export useful constants and functions from `lzma` for easy access: checks, filters,
etc.
:house: Internal
- Test that no warnings are generated
- Change development status to Alpha