This way, only one char's left and right edges are used, instead of its
(logical) neighbour's right edges.

In bidi content, this avoids trying to scroll to two logically close,
but visually far apart positions in some situations.

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