#34 XML Schema for validation/code completion

[Joseph Graves]

Automatically generate an XML schema to represent the
known valid tags and attributes for a test so that XML
editing code completion tools can be used to help in
test creation.

However, because we want the language to be extensible,
we want a means to allow people to use yet-unwritten
tags and concepts in the tests, so failing validation
against the XML schema should not prevent tests from
being saved or executed.