- Background parsing now never goes past the visible part of the
   document.

 - We only store style information for lines that are actually visible
   (and then keep it cached).

 - When the document changes, background highlighting always
   re-highlights from the change to the end of the visible part.

 - Gets rid of compareState mode methods and the hairy heuristic that
   tried to simulate it when absent.

 - The onHighlightComplete callback was removed, since it no longer
   really applies -- the document is only fully parsed when scrolled
   to its end.

This should help preserve memory (a huge document will no longer
immediately have parser state and highlighting information built up
for all lines, but only for the parts that you look at), and removes
the pathological case when you, for example, are typing at the top of
a huge XML document, and opening or closing a tag causes a whole
re-highlight to cascade all the way to the bottom because the
compareState will detect a change.

Issue #688

Fixes a problem where the editor would always be 30 pixels smaller
than its set height.

The height is now set on the outer wrapper DIV again, and some
height: 100% tricks are used to make height information flow
both ways (inside-out in demo/resize.html mode, outside-in in
normal, fixed-height mode).

Closes #775

Add CodeMirror.defineOption function for defining new options.

Add findMatchingBracket to the methods exported by this extension.

Closes #746

It is now more structured (knows about ranges) and allows automatic
unfolding when the cursor enters the folded range.

This allows multiple handlers to listen for a single event, and makes
the API a bit more uniform.

Issue #725

Issue #294

No more random {x,y,yBot} thrown into the mix.

- Multiple gutters are explicitly created with the gutters
  option
- Markers go into a specific gutter, new setGutterMarker,
  clearGutter methods
- The line number gutter is separate
- The 'fixedGutter' feature is removed (painful to do now,
  was shaky anyway)

(codemirror2 -> codemirror)

String.prototype.charAt returns '' (empty string) for characters outside the range of the string.

Suggested implementation for issue #722

Issue #721

This allows client code to find out which part of the document
is currently being shown.

This reverts commit b1431bd1.

I pushed it by accident.

This mode is based very heavily upon the javascript mode.