Update src/Tween.js

Tween#to should check if |duration| is undefined to default the parameter when it is not passed.
Merge pull request #61 from deanm/patch-1

Update src/Tween.js
Updated build.
Date.now() shim as suggested by @roshamb. Closes #62.
Updated build.
Testing TWEEN.Tween
Fix non-existing properties ending up in the tweened object as NaN
Test TWEEN.Tween.start() and TWEEN.Tween.stop()
Test TWEEN.Tween.delay()
Test TWEEN.Tween.easing(), onStart(), onUpdate(), onComplete() (last two fail for now)
Test TWEEN.Tween.chain with one chained tween
Tests: use TWEEN.update instead of manually calling TWEEN.Tween.update as that's the proper way of invoking the library
Test TWEEN.Tween.chain with several tweens
Test TWEEN.Tween.chain allows endless loops
Add test page for minified version
Add tests for TWEEN object
Add another test for TWEEN.update()
Rename 'l' with 'numTweens' or 'numChainedTween' as the 'l' got confused with '1'. Lowercase l is generally a bad choice for a variable name!
Update README with recent changes
Fix 06 -> 07 typo