Merge pull request #977 from jedesah/vect_length

Add length to Vect
Merge pull request #979 from david-christiansen/feature/apropos

:apropos improvements
Merge pull request #981 from david-christiansen/docs

Add some docstrings
Merge pull request #984 from david-christiansen/fin-add-mul

Addition and multiplication of Fin
Merge pull request #985 from david-christiansen/keyword-highlight

Add highlighting for keywords in interpreter output
Add a note to Vect.length about when to use it

Also add some other docs while I'm at it
Support text formatting in docstrings

Now, Markdown text formatting is no-longer a no-op. Needed to make the
stern warning on Vect.length look reasonable.