Implemented normalization

Simple
+ added normalize method which does the actual normalization

Document
+ added the normalizeDocument method

Node
+ added the normalize method
Implemented node.baseURI property

Simple
+ added ‘prop’ meta property, which is used by type 9 instances
(representing Document nodes). Ensure population of prop.uri with
either the passed on file name, or if none, the current working
directory of the app.

sax
* always pass an initialization object which provides the uri used for
baseURI

Node
+ implemented the getter function for the baseURI property
Implemented element.hasAttribute

Element
+ implemented the hasAttribute method
Implemented the getter for node.textContent
Clarified implementation documentation

Node
* isSupported (now always returns false, as in ‘not supported’)