Issue #1084
Issue #1630

Closes #1133

    Use newlineAndIndentContinueComment by default, falling back to newlineAndIndent if the former command is not defined.
    Same behavior is made default for Enter key in insert mode.

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

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

Since v2 is the canonical CodeMirror at this point

This is mostly a copy of demo/emacs.html.

So that I can put other doc-related stuff there without polluting the
root dir.

It's tiny anyway, no need to force people to include yet another file.