Release process

Tests: tox
Update CHANGELOG.rst, removing "(in development)" and adding date
Update the version number in ical2orgpy/__init__.py
Commit
Release to PyPI:
```
./release.sh
```
Tag the release e.g.:
```
git tag 0.5
```
Update the version numbers again, moving to the next release, and adding "-dev1"
Add new section to CHANGELOG.rst
git push --tags