Expand agent state transition coverage.

[Robadob]

Closes #169

May wish to rename conditional-behaviours.rst to agent-state-transitions.rst, however that will kill old links. @ptheywood has suggested there's Sphinx plugins to redirect old pages.

[ptheywood]

sphinxext-rediraffe works for full-page redirects (i.e. page renaming).

Needs:

• adding to requirements.txt

• add to the list of extensions in conf.py.in

• add a dict named rediraff_redirects to conf.py.in, with the old .rst path as the key, and new rst path as the value. i.e. (with full paths rather than just file names)

  rediraffe_redirects = {
      "conditional-behaviours.rst": "agent-state-transitions.rst",
  }