Setuptools-rust

- Remove python 2 support. [53](https://github.com/PyO3/setuptools-rust/pull/53)
- Fix compatibility with `cffi`. [68](https://github.com/PyO3/setuptools-rust/pull/68)
- Add support for pyo3 `0.12`'s `PYO3_PYTHON` setting. [71](https://github.com/PyO3/setuptools-rust/pull/71)

- Fix tomlgen\_rust generating invalid `Cargo.toml` files.
- Fix tomlgen\_rust setting wrong path in `.cargo/config`.

- Added license file [41](https://github.com/PyO3/setuptools-rust/pull/41)

- Add `html-py-ever` example

- `path` in `RustExtension` now defaults to `Cargo.toml`

- Add `rustc_flags` and `verbose` as options
- Adopted black code style
- Moved changelog to markdown