Release procedure

Please proceed as follows:

• Merge master into the develop branch (if needed)
• Merge new features into the develop branch
• Run the tests!
• Change the version number in PyHEADTAIL/_version.py and commit the change
• Create a release branch and push it to the github repository:

git checkout -b release/v1.14.0
git push --set-upstream origin release/v1.14.0

• From github, open a pull request to the master
• Merge the pull request from github (requires approval from a second maintainer)
• Delete the release branch
• Pull the new master

git checkout master
git pull