Changes demo html page to fit in with other mode demos, link from
project page and compression helper.

Courtesy of Daniel Glazman

In some modes, when querying a visibility: hidden node inside of an iframe,
IE8 and 9 will return nonsense coordinates.

It was confusing the compressor.

I'll have the release script add that from now on.

Example: a.do = 3;
 "do" is highlighted as a keyword.
Solution: do not classify identifier as a keyword after the "." operator.

Since v2 is the canonical CodeMirror at this point

Courtesy of Alexey Kolosov

Closes #283

Added getTextarea() method which returns the original textarea element when CodeMirror is instantiated using fromTextarea() method.

Context in pull req #281

This should prevent problems with parts of the document having a 'corrupt'
state when quickly scrolling down a big document.