Determine a style guide

[MrCreosote]

Discussion started here: #296 (review)

Style for for specifying and calling methods / functions:

Do some research into best practice for method signatures. E.g. I remember some people arguing for making all arguments keyword arguments for backwards compatibility reasons - you can shuffle your arguments around, make arguments optional, add new arguments, etc. and code doesn't break.

[bio-boris]

Style guide contents should also include whether we are following this pattern or a different one.

cfg['key'] == required value
cfg.get('key') == optionally None
cfg.get('key','default') == explicitly set default

[MrCreosote]

Related to the above comment: #304