New XML generating code.

This introduces dynamic generation of XML commands so there is
no need for most of the constants at the end of core.py. Adds
a new prettify utility to utils, and fixes a bug in __init__.py
(Exceptions have moved)
Service docstrings
Changes to core for the new services code
Fixing line_in and a few typos
Docstring for Queue service
Merge pull request #51 from lawrenceakka/new-services

The new XML services code
Merge pull request #52 from lawrenceakka/new-core

Changes to core for the new services code