* Improved Blockly.XML comments.
* Support JSDOM as an alternate parser under Node.js
* Throw standard errors instead of goog.asserts.
* Adding textToDomDocument_ and override in gulpfile.
Build depends upon ../closure-library, which is outside the usual
npm process. And since the library ships pre-built, just concatenate
the built files to make the node-ready version.
The gulp file is derived from work in PR #887, with numerous
refinements and clarifying comments.
Also updating the version number in package.json, including the
'develop' prerelease tag for the develop branch.
