Markup links on 'enter' too.

* Check for links in the current text node, and add <a> tags if found, when the
  enter key is pressed, not just when the spacebar is pressed.
Update Makefile to use uglifyjs2.

* Takes different options as parameters.
Catch all errors to allow logging.

* All errors will be caught and passed to the editor.didError fn. This can be
  overridden to do something useful, like logging them to the server.
Set `build` as default Make target.
Make Element#getPath more robust.

Won't throw an error if called on a node that is not part of a document, but
will now instead return the path from whatever the root element is down to the
node.
Fix bug in Range#insertTreeFragment

Merging containers could remove the nodeAfterSplit from the tree, which then
caused an error to be thrown if it had no content, as the code would try to
remove it again.