remove diff from readme
Add analytics to readme
fix size dirty checking

`_sizeDirty` was always false, and there was a typo when checking if there is a size
Add getSize to ScrollContainer
verify existence of performance.now
Remove References to submodules from README
Update Contributing to no longer reference submodules
Update emails in travis.yml
Fix linter to fail on eslint

Originally we were not explicitly running one linter after another, and if eslint failed it would not trigger a failure on travis.
reference window.performance.now rather than global performance
sizeDirty flag removed
change DEFAULT_OPTION direction to Y
core/Entity: Fix typos
Corrected setSize size parameter documentation
Corrects transition documentation in StateModifier
Simple link update on Physics's README.md

Nothing fancy.
Reset the opacity for target
Set _opacity to null on setup
Fixed typos in function documentation and errors

Function descriptions/documentation and corresponding errors were not always referencing the correct function. This is now fixed so that it is clearer to the user.
Reset origin dirty flag on setup