Seq-to-first-iso

*Added*
- Flag for version number in CLI
- Jupyter notebook with Binder environment for demonstrations
- Documentation on Read the Docs
- Disponibility on conda

*Changed*
- **Breaking change** : changed seq_to_midas() to seq_to_xcomp()
- **Breaking change** : changed seq_to_tsv() to seq_to_df()

*Fixed*
- Fix requirements not being installed with `pip install`

*Fixed*
- Fix *setup.cfg*'s installation requirements

- Extend numpydoc style to all functions in *seq_to_first_iso.py*

*Changed*
- Add support for Xtandem Parsing
- **Breaking change:** sequence_parser() now returns a dict with "annotations", "raw_sequences", "sequences", "modifications" and "ignored_lines"
- Add get_mods_composition() that returns a composition from a list of Unimod PTMs
- Remove the appended "\_stfi" if -o flag is provided

*Changed*
- Add support for files with annotations before the sequences
- **Breaking change:** sequence_parser() now returns (annotations, sequences, ignored_lines)
- seq_to_tsv() now accepts (sequences, unlabelled_aa, annotations=None)

*Fixed*
- Output files now have "\_stfi" appended to differentiate from .tsv input files with the same name