Updated TODO.
Allow passing an Int code to content error state

This allows us to error on codes other than 400.
Added code to XPath in XSD.
Added builder code to add the code XPath state.
Modify the XPath Sate to accept code, handler passes code over.
Make xpath join opt (and xsl mode) aware of xpath code attribute.
Initial state tests for rax:code in plain params.
Added checker tests for rax:code extension.
Whoops, fixed bug where error code not retrived correctly from xsl step.
Added validator tests on rax:code extension.
Merge pull request #106 from InABlender/error_code

Custumizable error handling In Plain Parm