Nanoset

Fixed
- Bumped `pyo3` to `v0.11.0`, which should fix thread-safety issues.

Added
- `NanoSet` and `PicoSet` are now `collections.abc.MutableSet` subclasses.

Changed
- Bumped `pyo3` to `v0.10.1`.

Fixed
- Potential garbage collection crash caused by older `pyo3` versions.
([pyo3855](https://github.com/PyO3/pyo3/pull/855)).

Added
- Compilation of Python 3.5 and 3.8 wheels for Mac OSX
([3](https://github.com/althonos/nanoset.py/issues/3)).

Added
- Special case to create a `NanoSet` from a `dict` without rehashing.
- Implementation of equality check from `NanoSet` to `frozenset`.

Fixed
- Compilation of Rust crate when not building a Python extension module.
- Project metadata for PyPI and `crates.io`.
- OSX deployment scripts not deploying built wheels successfully.

Added
- `pyproject.toml` file to source distribution.