Don't double-escape style names

Previously we were escaping both in createMarkupForStyles and then in createMarkupForProperty; now we escape only in the latter (otherwise the hypothetical style name `b&ckground` would become `b&amp;amp;ckground`).

Test Plan: grunt fasttest
Merge pull request #1464 from spicyj/style-esc

Don't double-escape style names
Expose React.addons.Perf
Fix example for animation

* Highlight the correct lines
* Add missing text to button
* Remove unnecessary div
Merge pull request #1731 from cody/master

Fix example for animation