Crowsetta

added
- `data` module that downloads small example datasets for each annotation format
+ includes `formats` function that is imported at package level
and prints formats built in to `crowsetta`
- `to_seq_func_to_csv` that takes a `yourformat2seq` function and returns a function
that will convert the same format to csv files (just a wrapper around your function
and `seq2csv`)
- for docs, Makefile that generates `./notebooks` folder from `./doc/notebooks`

changed
- major revamp of docs
- `config_dict`s for `user_config` arg of Transcriber.__init__ only require
`module` and `to_seq` keys; `to_csv` and `to_format` are optional, can be
specified Python `None` or a string `'None'`

fixed
- Transcriber raises `NotImplemented` error when `to_csv` or `to_format` are
None for a specified format (instead of crashing mysteriously)
- `seq2csv` and `csv2seq` can deal with `None` values for one pair of onsets and offsets

changed
- fix failing tests

added
- `Segment` class, attrs-based
+ has `asdict` method (wrapper around `attrs` function)
+ has class variable `_FIELDS` which is used in any place
where we need to know how to go from `Segment` attributes to rows of
a csv file, e.g. in src/crowsetta/csv.py and in tests

changed
- `Sequence` class is now attrs-based, has factory functions, is itself
just a list of `Segment`s
+ now has `to_dict` method
- `Crowsetta` class is now called `Transcriber`

added
- add Crowsetta class with simple interface for converting any annotation to
- add ability to work with user-defined functions
+ user passes an `extra_config` dict when instantiating Crowsetta
- add docs

changed
- change package name to Crowsetta
- change function names so they are all 'format2seq' or 'format2csv' or
'toformat' for consistency

- Initial version after excising from hvc
(https://github.com/NickleDave/hybrid-vocal-classifier/blob/master/hvc/utils/annotation.py)

changed
- Convert tests to Python unittest format (instead of using PyTest library)

added
+ Write README.md with usage