Fixes #3449

Closes #3170

Issue #3127

As long as CodeMirror.normalizeKeyMap is called on them before they are
used. This interface is a little weird, but backwards-compatible.

Closes #2723

Bumping them for every release just adds too much git
noise and history blowup.

Issue #2542

Issue #2448

Closes #2348

Issue #2380

Issue #2354

"Shift-Ctrl-K"            Delete line
"Ctrl-K Ctrl-K"           Delete line to right
"Ctrl-K Ctrl-Backspace"   Delete line to left
Swapline                  scrolls with the cursor

Issue #2354

Issue #2362

Also add origins to the changes generated.

This makes it easier to update selections by mapping over them.

It should duplicate for every selection, and for non-empty selections
only duplicate the selected text.

Also, wrap the command in an operation and use the head rather than
the anchor of the selections.

Since it's what you want most of the time, and easy to forget.