Implement Git Flow branching model

[gaurav]

We currently use a slightly simplified version of the Git Flow branching model -- we create feature branches to develop new features with tests, and then merge them into the main branch once they are complete. Going forward, it would be useful to separate the develop branch from the main branch, so that the main branch remains in sync with the latest version of the software deployed to https://cancerdhc.github.io/ccdhmodel/ and https://pypi.org/project/crdch-model/. If we do this, we might as well deploy the full Git Flow branching model, which additionally provides useful support for:

• Creating versioned releases with CHANGELOGs
• Creating "hot fix" branches when minor changes need to be made to deployed software

I would recommend using the GitFlow Git extension (https://github.com/nvie/gitflow) to implement this branching model locally, and I can organize a mini demo session to walk you all through this model if that would be useful.