hero.detach - Githubissues

This PR adds documentation that was missing from the previous "commit" PR.

It also implements a number of changes to the "commit" PR in order to simplify concepts/usage.

HeroExtractor has been renamed to HeroReplay.
The previous concept of FrozenDOM has been renamed to DetachedDom.
element.$extract has been removed.
element.$collect has been renamed to element.$detach
hero.collect has been split into two methods:
- hero.detach allows detaching elements and resources.
- hero.setData allows saving arbitrary JSON-able data to the session db
CollectedElements has been renamed to DetachedElements
CollectedResources has been renamed to DetachedResources
CollectedSnippets has been replaced with hero.getData

ulixee / hero