Add Xml Parser shadowing copy in Std.  Going to do some fixes
Fairly major fix of html entity handling

Still not perfect, but much better.

- Standardize on: escaped html in -> (DOM uses unescaped values) -> escaped html out
- On neko/cpp, use haxe.xml.Parser instead of Xml.parse() if there are entities
- Use a modified haxe.xml.Parser to make sure we unescape entities in attribute values
- These fixes affected alot: html() innerHTML() text() clone() etc
- Fix for widgets, the entity handling there was just a mess
- Add many tests to standardize behaviour
- Fix broken tests after the changes

Currently JS and Neko pass.  C++ has an unrelated failure in it's widgets (was there before,
separate issue).  Flash is pretty dodgy with a lot of failures.  I think I should drop
official support until I can do a better abstract over flash.xml.XML or whatever it is...

This may cause some breaking changes if you relied on it encoding entities
for you before.