Fixed transcription error for sulfur experimental Hf

Enthalpy of formation should be 65.66 kcal/mol, as in Gaussian
whitepaper.  Also added bond additivity correction for S-H
(even though it's 0).
Adding sulfur atom energies for CCSD(T)-F12.

Adding sulfur atom energies for CCSD(T)-F12a and F12b, with the
basis sets cc-pVDZ-F12, cc-pVTZ-F12 and cc-pVQZ-F12
Changing incorrect comma to colon.
Merge pull request #269 from cclass86/sulfur

Updates to sulfur thermo in statmech.py
More edits in input file documentation…
update documentation users/rmg/thermo.rst

add some images too.
move general info on RMG databases to dedicated introduction.rst file

instead of having it inside kinetics.rst.
This info also applied to thermochemistry.
update users/rmg/database/thermo.rst documentation
add parts on symmetry, chirality, QMTP file types in thermo.rst docs
add thermoEstimation module documentation

copy QMTP part in users/rmg/input.rst into the module
documentation of the thermoEstimator.
fix some minor errors in thermo docs
Redirect documentation link on heirarchical tree structures.
Fix charges and lone pairs for Helium in fromAdjacencyList() and updateCharge().

Also made calculating charges no longer redundent since it is done in updateCharge().
Special inchi handling for both H and He.
Add a Helium unit test.
Merge pull request #273 from connie/master

Fix handling of Helium in RMG-Py. Looks good to me, and passes Travis tests.