Open Sourcing PR

[zcmarine]

This commit copies over the code from Squarespace's internal pgbedrock repo to this public repo. The code for pgbedrock itself remains unchanged, though the README and deployment machinery have been modified. More specifically, this commit adds the ability to push versioned releases to quay (for docker) and pypi (for Python). Note that the pypi release process is untested as we need a version ready before we can test pushing. In addition, I've also added a bit more detail to the README.

As this code has gone through 2 PRs already within the internal Squarespace repo, this PR is mostly ceremonial.

After merging, I will be running:

• git tag 0.1.0 -m 'Initial release'
• git push --tags origin master
• make release_quay
• make release_pypi

[cpdean]

lgtm

:shipit:

[punkrockpolly]

slight nitpick: pep8 convention is that docstrings use """ instead of '''