Support AtomsMaya >= 6.2

Merge pull request #53 from yannci/atoms6BuildAdjustments

Atoms version 6 build adjustments and support for Gaffer 1.3 with OpenEXR version 3

Merge pull request #51 from yannci/fixVariationNameClash

AtomsCrowdGenerator: Fix clashing agent variation names

Merge pull request #50 from andrewkaufman/pie3

Python 3 Support

Merge pull request #49 from andrewkaufman/gaffer60

Updates for Gaffer 0.60

Merge pull request #44 from fdagenais-cinesite/fix_affects_methods

Fix dirtying issues in affects() methods

Merge pull request #42 from andrewkaufman/buildImprovements

Build improvements

Merge pull request #38 from andrewkaufman/cachePolicy

Protect engine plugs with the Gaffer 0.54 computeCachePolicy

Merge pull request #9 from iaiotom/meshAtoms3

Added support to the new mesh format of atoms 3

Merge pull request #7 from ivanimanishi/improvedPythonBindings

AtomsGafferModule: Bindings allow subclassing in python