Closes #1992

Closes #1133

In order to not duplicate all its logic.

Issue #751

As spotted by the extended linter.

And move closetag over to it.

This makes the code that gets the XML state out of the mode actually
sound and extensible.

Issue #820

Add CodeMirror.defineOption function for defining new options.

Add findMatchingBracket to the methods exported by this extension.

Closes #746

The space between "return" and "die" was missing causing both to not get
highlighted. While in there I removed "cfunction as it was PHP4 only,
added "trait" (coming in 5.4), and added "__halt_compiler", "self",
"static", and "parent".

You will confuse the outer HTML parser if you do really weird things,
though.

Since v2 is the canonical CodeMirror at this point

This way, if you load the htmlmixed mode before the PHP mode, it won't
try to use that.

So that I can put other doc-related stuff there without polluting the
root dir.

It's tiny anyway, no need to force people to include yet another file.

Closes #207

Instead of hard-coding all kinds of language-specific behaviours in the
mode itself, specializations can now pass character hooks to implement
their own highlighting.

This normalizes the classes used by most of the modes
(reStructuredText and diff didn't fit in), and makes them all
reference a central style sheet (under theme/). It also adds a theme
option that can be set to change the theme, and defines a few
different themes (some based on old mode colors).