WIP: Cleanup chemkin module

I'm pushing this as a heads-up that I'm churning this section of code
(let me know if someone else is working here, and I'll wait until
they're done).  Don't merge it yet ;).

While reviewing #213 I noticed a wildcard import (from … import *),
and thought I'd take a moment to clean it up.  However, my first pass
at that (through chemkin.py) turned up a number of large, complicated
functions that could use some refactoring.  This series is my attempt
to polish up the Python in chemkin without breaking any of the logic
that I don't particularly understand ;).  I'll push periodically so
Travis can see if I broke anything, while I try to split this logic
into easily-digestible bites.