closes #993

Closes #1095

Issue #1079

* and # will fall back to non-blank characters if no keyword is found.

moveByLines was changed to better keep track of the previous
action.  For example, if moveToEol was the previous action,
moving up or down should stay at Eol regardless of line length.

See discussion in https://github.com/marijnh/CodeMirror/pull/984

Closes #995

Useful for add-ons that need to register keys.

The 'inverted' hack which hailed from the ancient times when selection
was handled by the hidden textarea, has been replaced with a saner explicit
anchor and head. setSelection now directly sets the anchor and head, rather
than always creating a forward selection.

I give up.

Issue #923

Things that happen in a single operation are now always combined into
an undo history event. Subsequent typing or deleting is combined, if
it is close together in time, even when done in separate operations.

Closes #889

Also stores old selection position in undo history, restoring it
when applying a changeset.

Issue #923

Cut down on round-trips (and improve caching) by measuing all
characters in a line at once, and caching the resulting object, rather
than forcing an (expensive) DOM layout for every char that is
measured, and caching per-char.

That were used to find the precise width at which something wraps.

To allow arbitrary folding of text, and replacement with widgets.

Remove old line folding system.