Use the document load event as the zero point for document time

Also make sure that the document time is null before this zero point, and add a
test to check that the document time is constant within a JavaScript
callstack.

This fixes https://github.com/web-animations/web-animations-js/issues/101
Merge pull request #102 from steveblock/zeroTime

Use the document load event as the zero point for document time
Rename web-animation.js to web-animations.js

Also rename web-animation-test.html to web-animations-test.html and
web-animation-visualization.js to web-animations-visualization.js.

This fixes https://github.com/web-animations/web-animations-js/issues/113
Merge pull request #119 from steveblock/rename

Rename web-animation.js to web-animations.js
Merge pull request #118 from dstockwell/test-cases

Move list of test cases to a separate script and add update utility
Update test-compositing-order.html to use new Player syntax
Fix test-compositing-order.html

This intent of the test was broken by 1e21b9ee86fb7225494257a787dc9e0fbb5a01a5
though the test continued to pass.
Change compositing order to match new spec

For compositing, we now sort animations first by Player start time, and second
by DFS order within the Player's tree.

This fixes https://github.com/web-animations/web-animations-js/issues/100
Merge pull request #122 from steveblock/compositing

Change compositing order to match new spec
Clean up some hotspots