servo / html5ever

Auto merge of #184 - servo:string-cache-up, r=asajeffrey
Upgrade string-cache to 0.2.

r? @asajeffrey

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Auto merge of #142 - servo:tendril-v2, r=SimonSapin
Zero copy parsing take 3

This includes the [tendril](https://github.com/kmcallister/tendril) integration which is desired for `document.write`. The only missing piece afaik is fixing up the C API (or temporarily disabling it, but I'd rather not).

I won't have time to finish up this PR but I can answer questions for sure.

(Was #141.)

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Make html5ever not depend on html5ever_dom_sink
Move some tests.