fn:doc() support

[Vinayak Borkar <vb...@yahoo.com>]

Guys,

I have checked in support for fn:doc(). The ground work to represent the 
6 different XML node types as bytes (that Till and I spent the last few 
weeks building) is also in to support the fn:doc() function.

Currently, the only thing you can do is to use the doc() function in a 
query to parse in an XML document. Functions that evaluate path steps or 
that serialize XML nodes into text XML have not yet been implemented.

Initial analysis shows that the binary representation of documents 
occupies about 2 to 2.5x the size of the original XML file. Further 
optimization is possible, but the next step will be to focus on getting 
more functionality in place.

Please let me know if you have any thoughts or comments.

Thanks,
Vinayak