Closes #1026

    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.

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.

This adds a blankLine method that calls the current mode's blankLine if
it has one. It has allows switching on a blank line if "\n" is specified
for "open" or "close".

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

Closes #995

Useful for add-ons that need to register keys.

array initialization (one entry per line) results in extra indentation from second element onwards:
ex:-
const string[] fields = {
  "one",
    "two",
    "three"
};

Issue #986

Issue #986

This stores the previous value for a mode property if an extension
overwrites it with a new value. The old value is stored in a property
prefixed with an underscore (e.g. "_token"). This allows extensions to
piggyback the old value by still being able to access it.

This allows the xml mode to return a style with space separated classes
and still work. I didn't use /\btag\b/ since that can match "tag-foo".

Closes #1002