Added (preliminary) doctype support, moved from node-expat to htmlparser2, updated to lab 5 for unit tests

lib/dom.js
lib/processor.js
lib/processor/handler.js
* switched xml/html parsing from node-expat to htmlparser2, which is in much more active development (might switch to parse5, which is currently in development and might replace htmlparser2) and doesn't affect performance by much

lib/dom/document.js
lib/dom/documenttype/.js
+ added support for doctype, this support is preliminary, as entity declarations are not yet supported.

*/sax.js
- removed sax (node-expat) wrapper and its tests

test/*
* moved to lab 5, which completely overhauled the assertions