Release procedure

In brian2tools we use the setuptools_scm package to set the package version information, the basic release procedure therefore consists of setting a git tag and pushing that tag to github. The test builds on travis will then automatically push the conda packages to anaconda.org.

The dev/release/prepare_release.py script automates the tag creation and makes sure that no uncommited changes exist when doing do.

In the future, we will probably also push the pypi packages automatically from the test builds; for now this has to be done manually. The prepare_release.py script mentioned above will already create the source distribution and universal wheel files, they can then be uploaded with twine upload dist/* or using the dev/release/upload_to_pypi.py script.