Since moving the highlighting frontier forward when doing
things like getTokenAt is not safe at all.

Also properly update highlighting frontier when a change
happens.

Issue #4800

Closes #4786.

So that Doc can do its auto-new trick before calling the
superclass constructor.

Closes #4768

Closes #4760

FEATURE: Mouse button clicks can now be bound in keymaps by using
names like `"LeftClick"` or `"Ctrl-Alt-MiddleTripleClick"`. When bound
to a function, that function will be passed the position of the click
as second argument.

FEATURE: The behavior of mouse selection and dragging can now be
customized with the
[`configureMouse`](http://codemirror.net/doc/manual.html#option_configureMouse)
option.

Issue #4727

This closes #4691 and is based on an idea by Joel <joel.einbinder@gmail.com>.

Issue #4724

Issue #4726

I broke this in 0ad53e0a. Closes #4713.

To work with Chrome's overlay scrollbars

Issue #4676

Issue #4694

Issue #4694

(When the mouse didn't move.)

Closes #4677

Closes #4657

Issue #4625