How to do releases

Make sure you are on master branch, and have pulled latest changes.
Check test suite passes on all supported versions:
```
tox
```
Change docs/history.rst to remove " - unreleased"
Update the version number (removing the -dev1 part):
- src/parsy/__init__.py
- docs/conf.py
Commit with "Version bump"
Release to PyPI:
```
$ ./release.sh
```

Post release

Bump version numbers to next version, and add -dev1 suffix, for example 0.9.0-dev1
Add new section to docs/history.rst, with " - unreleased".
Commit and push