Bump version to development version 1.1.1.
Remove obsolete clean target.
Always check that MorphoDiTa library is up-to-date.
Add strip_lemma_comment and strip_lemma_id tag set converters.

- Add the converters to public API.
- Add the converters to executables (update usage and docs).
- Add the converters to bindings API.
- Refactor tagset_converter instances because all need to filter duplicities.
- Update docs.
- Update CHANGES.
Release stable version 1.2.0.