Create python script for making release

[gavv]

Currently, release creation involves these steps:

• open version.go and update bindingsVersion to new version X.Y.Z
• commit this change
• create git tag vX.Y.Z
• push branch and tag
• wait until CI for git tag passes and creates github release
• edit github release changelog and publish release

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It would be convenient to automate the first half of this procedure. We could create a new script tag.py used as follows:

./tag.py 0.2.1

or:

./tag.py --push origin 0.2.1

This script will:

• verify that its command-line argument have correct form (int.int.int)
• verify that the specified tag does not exist yet
• update bindingsVersion in version.go to the specified tag
• commit this change
• create git tag with specified name
• if --push is given, push the change and the tag to specified remote (e.g. origin)

The script should be cross-platform (thus python).

---

After doing this, release procedure will look as follows:

• run ./tag.py --push origin VERSION
• wait CI
• edit github release changelog and publish release

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We'll need to document (briefly) the new procedure in README.