Fixed incorrect units in CharmmCrdFile
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