Add TextString.toJSON().
Renamed dm.Surface.moveCursor to createRelativeRange.
Adapt to changes in dm.Selection.
Return node after creation.
Add properties 'from', 'to' to dm.Selection.
(Re-)Add dm.Surface.setSelection().
Getter for Surface.container.
Allow string input for Surface.insertAt for sake of convenience.
Fixed html2json converter.
Updated test samples.

- changed node ids in 'simple'
- added 'two_paragraphs'
Added Surface tests.

- editing
- cursor movement