Small change to input doc for rmg familes

Just made it a little clearer that the 'default' option is just a
string, while multiple Families are designated as a list of strings
Tweak the chemkin docstrings and documentation.

Written by: Enoch Dames <enoch.dames@gmail.com>
Rebased by: Richard West <r.west@neu.edu>
Make CanTherm alert user if reacting species is not lowest E conformer

For large molecules, it's not always easy to know that the species you
use during a reaction is at it's lowest energy conformation. However,
the scan calculations that are used for inclusion of hindered rotors can
be used to alert a user if this is potentially the case, since most/all
users utilize the geometry from one of their reacting species to
initiate a scan calculation.

This commit now incorporated suggestions by @nickvandewiele
Merged and rebased by Richard West <r.west@neu.edu>
Added a CanTherm example for methoxy decomposition to H + CH2O.

Commit by: Enoch Dames <enoch.dames@gmail.com>
Signed-off-by: Richard West <r.west@neu.edu>
Added a bunch of CanTherm unit tests.

Written by: Enoch Dames <enoch.dames@gmail.com>
Rebased by: Richard West <r.west@neu.edu>
Help CanTherm unit tests find the input file.

If you're running it from a different root directory, eg. via nosetests
or `make test`, this helps it find the input file.
(Not sure where we should put input files like this, but this works for now.)
Merge branch 'pr/287' to get Enoch's CanTherm fixes, examples, and tests.

This closes #287.

1) It now alerts the user if they are not using the lowest energy conformer
   (based on the hindered rotor scans).
2) There is an example for methoxy decomposition.
3) There are some unit tests.
Fix the make test failure

The problem is nosetests was discovering the methoxy.py cantherm
input file inside the rmgpy/cantherm/test/ directory, and because
it was inside a directory called 'test' it was trying to run it
By Renaming the directory atest we stop this. Bit of an ugly hack.
An alternative would be rename that one file so it doesn't end in
.py (eg. methoxy.cantherm)?