Added cantherm module to read in QChem output files

qchem.py: this new module works reads in information from qchem output
files (e.g., opt+freq jobs, PES scan jobs). In it's present form, it
works, but there is still one more thing that must be added - a read
force constant matrix function. I've been advised to make this commit
earlier rather than later, however. statmech.py is necessarily changed
so that RMG/cantherm recognizes qchem files. In addition, I know I still
have to make unittests, and update the documentation, which I'll get to
shortly. Feel free to test it out and let me know what's wrong.
Updates to qchem module for CanTherm

Mostly bug fixes.
fixup for reading in atomic number in cantherm

didn't realize the qchem mod was not properly reading in atomic numbers.
Caused cantherm to crash when trying to write cartesian coordinates of
species to the output file
Added another example reaction

my isopentoxy example is too big (it has 30+ MB of qchem output files),
so I am adding a smaller one. I will add other small ones in the future
that include pdep. Also, I reverted a change in the C2H4+H example back
to what is on the master RMG-Py brach.
added another example to cantherm

this one is for a unimolecular decomposition reaction using the Qchem
mod
Merge pull request #256 from connie/qchem

Qchem Module for Cantherm.