Fastobo

Added
- Wheel compilation for older OSX versions.
- Automatic download on UNIX platforms for platforms without `rustc` installing
from source distribution.

Changed
- Bumped `fastobo` to `v0.10.0` to support comment lines.
- Bumped `pyo3` to [`v0.11.1`](https://github.com/PyO3/pyo3/blob/master/CHANGELOG.md#0111---2020-06-30).
Fixed
- `fastobo.id.parse` will chain the eventual `SyntaxError` to the `ValueError`
raised if the identifier is invalid.
- Python threads are now released during intensive operations running only
on the Rust side.

Fixed
- `OboDoc` not implementing list methods (`.append`, etc.).

Changed
- Bumped `fastobo` to `v0.9.0`.
- Bumped `fastobo-graphs` to `v0.3.0`.
Added
- `fastobo.id.is_valid` function to check whether or not a string is a
valid OBO identifier.

Changed
- Bumped `fastobo` to `v0.8.4`.
- Bumped `pyo3` to `v0.10.1`.
- Removed occurences of unsafe code for Python type management.
- Reduced number of GIL acquisition where possible.
- Changed implementation of file wrappers to use `PyAny` where applicable.
Added
- Configuratble support for multithreading in `fastobo.iter`, `fastobo.load`
and `fastobo.loads` using the `threads` keyword argument.

Changed
- Bumped `fastobo` to `v0.8.3` to fix `Display` implementation of
`fastobo::ast::IsoDateTime`.