formulaParser various bug fixes
fix formulaParser example
optimize formulaParser to prevent creating useless utility nodes
refactoring + various bug fixes

- rename autorig core variables (aInput->inputs, oGrpRig->grp_rig,
oGrpAnm->grp_anm, etc)
- upgrade libPymel.[hold/fetch/rename]Attr
- fix bugs in libSerialization
- add basic unitTest for unitTesting autorig