Improve unit handling in charmm crd file classes.
Merge pull request #477 from swails/fix_charmm_crdunits

Improve unit handling in charmm crd file classes.
Add virtual sites
Out of plane
Merge pull request #478 from mpharrigan/vs

Add virtual sites
Created CustomNonbondedForce::createExclusionsFromBonds()
ForceField supports CustomNonbondedForce
Added documentation for using a CustomNonbondedForce in force fields.  Also updated documentation on how to specify a tabulated function.
Make sure that calling createExclusionsFromBonds() with bondCutoff=0 never adds exclusions
Merge branch 'master' of https://github.com/SimTk/openmm into exclusions
Reverted a change that is no longer necessary
Merge pull request #481 from peastman/exclusions

Force field XML files can specify CustomNonbondedForces
GromacsTopFile adds exclusions based on [ exclusions ] directives
Merge pull request #482 from peastman/gmxexcl

GromacsTopFile adds exclusions based on [ exclusions ] directives
Fix PSF parser in cases where single residues are differentiated by their system
(which means that consecutive residues may have the same residue number _and_
name, but are different residues).
Merge pull request #483 from swails/fix_charmm_psf

Fix residue assignment in PSF parser