Courtesy of Cliff Koh

Turns out we have to prevent the default action of the event to get into our custom code.
Also, loadFile has to be declared before we can call it, otherwise we get a function not defined error.

Select nodes aren't guaranteed to have a value property

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).

Doing shift-left-arrow a few times and then shift-up a few times,
you'd get weird jumping selections as you went up.

(Which would make horizonal scrollbars 'stick' after the wide lines had
been deleted.)

See comment in code for details. Fixes #90

This remove the ugly white square popping up right before the
context menu opens on right-click.

This prevents the 'flicker' of black text when typing in coloured
elements.

It would raise an error on a hidden editor because showingTo was 0,
causing no HTML to be produced, although further code assumed there
would be at least one number.

Fixes #110

It causes random cursor movement and text deletion for some
reason.

Fixes #105

When the selection included the end of a line, and you typed a
character, it'd get the offsets wrong and duplicate the part of
the line before the selection.

Fixes #111

This to solve issues with 'CSS reset' packages that gave PRE nodes
a padding.