Merge pull request #28 from bas-rustenburg/master

Added support for net_charge override to run_antechamber.
Working packmol code
Fixed some doc
Can't use example for packmol because it breaks doctests
Added testing for packmol location
Added exception handling for packmol finding
Delete some extraneous code in packmol
Improved docstring in amber parser init
Reverted unneeded change to antechamber cmd line
Fixed unnecessary tab.
Added openbabel and rdkit to travis
Typo in packmol find path
Add some sanity checks to smiles unit test
Merge pull request #32 from choderalab/molpack

[WIP] Several Fixes, Changes, and PackMol support.
Allow name override in smiles to xml
Fixes for multiple ligand XML files.
Merge pull request #43 from choderalab/fixsmiles

[WIP] Multiple ligands in single ffXML file
approximation for initial box size