Partition style rules into a few tags

@contra: now that ie8 is supported, there's also the 4095 rules per style tag limitation apparently: http://stackoverflow.com/questions/9906794/internet-explorers-css-rules-limits

I'm also a bit worried about parsing time. Re-evaluating the style string can become very expensive?

The issue names no files, tests, or entry points; begin by locating the code that creates style tags and re-evaluates the style string. Define how rules should be partitioned and how repeated parsing is avoided, then verify behavior in Internet Explorer 8 and check parsing performance.

Written by the indexing model from the issue text.