Graph-state-machine

Misc 3.x work:
- Reworked necessity and sufficiency attributes to be more flexible (now node attributes rather than edge ones for convenience).
- Improved plotting
- Added conditional steps (i.e. the option to execute only if no nodes of the requested type are already in the state)

Plotly is now the default plotting backend; radial node labelling is an option.
Internal node-filtering changes.

(Fixed a bug in v2.0, amended the commit and deleted the release)
NOT backwards-compatible: the old step methods (and scanner functions) took only one extra optional NodeType argument, while the current ones take multiple ones, of which the first is now a List of NodeType.

Examples of call changes:
Python
OLD parallel or consecutive steps methods syntax:
gsm.consecutive_steps(['Distribution', 'Family Implementation'])

NEW versions, named and unnamed (translating the above involves only the first of 4 optional arguments):
gsm.consecutive_steps(dict(node_types = ['Distribution']), dict(node_types = ['Family Implementation']))
gsm.consecutive_steps([['Distribution']], [['Family Implementation']])


OLD single step syntax
gsm._scan('Method Function')

NEW
gsm._scan(['Method Function'])

Jaccard similarity score by default, customisable plotting layout, more visible state highlighting, reported node type in failed-step warnings, improved readme and documenting-comments, automatic dependency installation, changed license from MIT to BSD 3-Clause.

Single-commit release; see commit message.

Debut; just read the README.