Begin automatic documentation

[paddy-r]

Create doc folder once new file structure established (see issue #3). Ultimate goal is to create self-documenting code in parallel with manual and readme.

• Start with doc folder
• Add some docstrings to step_parse for starters
• Choose output format via Sphinx
• Check deployment (via Github Pages or Read the Docs -> decide!)
• Add anything to .gitignore to tidy up
• Draw line when output looks good; then raise another issue to streamline readme, manual and automated (code) documentation into fewer processes/outputs