Release BuildStream on PyPi

Background

Current instructions to install BuildStream cloning the git repo, checking out the desired tag and doing a pip install --user .. If we release it on PyPi, we can cut down the process to a one-liner pip install BuildStream. Upgrading it would similarly be just pip install --upgrade BuildStream like any other Python package.

For managing releases, this should also give us an easy way to tell users how to install the latest stable release of BuildStream.

It is worth noting that this WILL NOT solve the distribution story for BuildStream. For that, see #332. The aim of this task is simply to make the pip install process more streamlined.

Task description

• Ensure setup.py has all the necessary metadata
• Release BuildStream on PyPi
• Release previous BuildStream versions
• Setup automation to handle releases in future
• Add documentation to the Install guide, this should become the preferred installation method instead of git.

Acceptance Criteria

One is able to install any versions of BuildStream released so far, using pip.

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