Slow, and problematic on several browsers.

Closes #535

(They slow down reading from it enormously.)

It'll create a 'call stack size exceeded' (??) error on Chrome

Closes #532

And highlight non-builtin symbols as "variable".

Closes #537

Closes #525

Issue #520

Closes #519

Issue #517

Which apparently assigns an offsetLeft of 0 to spans that are wrapped (rather
than using the offset of the first character, as other browsers do)

Closes #514

This is probably the first and only commit where
I deliberately *add* trailing whitespace (to show
off the feature here).

When typing at the end of a long line without line-wrapping, the editor
wouldn't scroll with the cursor.

Closes #511

Use this in the VIM mode to make the cursor wide in escape mode.

This makes it easier for alternative keymaps to hook into it.

$ now goes not till the end of line, but one symbol before it (so e.g.
$i works as in vim now)

define per-character key-bindings in a function, instead of a loop
(where local variable "m" was bound to the last value in loop - see
line 203 in original source - so the prefix-d' and prefix-y'
key-bindings were useless)

do not raise js error when mark is not set (for prefix-d' and
prefix-y' maps)

Added a list of implemented and major not implemented key-bindings at
the top

Added commands: de, dd, P, f, t, df, dt, F, T, dF, dT, cf, ct, cF, cT,
gg, s, ce, cb, r, D, cc

I hope to merge xmlpure into xml real soon now.