Release tagging mechanics

[pjbull]

For changes to defaults, we'll want well structured release mechanics.

This has come up since #387 is proposing changing defaults.

Here's a proposal for release mechanics:

• Develop feature branches PR'd into master
• Release regularly following semantic versioning
• Couple both ccds code + template changes together in a single version number (maybe we split these out later, but lets keep it simple for now)
• On release workflow, tag commit with version number
• Publish corresponding ccds package version number to PyPI
• Default ccds clones the template @ the version tag
• Add --latest flag to get the latest from master instead

Thoughts?

[chrisjkuch]

I think this sounds quite reasonable to me!