replace couchd update handler with simple python equivalent
delete now-unused _design updates/utils
add xml2json to travis requirements
fix tests to call the interface

instead of the update handler which has been removed
improve interface and minor cleanup

change name of post_from_settings to create_xform_from_xml
and expose as couchforms.create_xform_from_xml
raise explicit exception for invalid form xml

- new exception couchforms.XMLSyntaxError
  (Didn't just let the lxml error bleed through because
  that would be tying the API to an implemenation detail.)
- add short docstring indicating exception raised
fix catching of xml syntax error

refactor to use xml2json (python) broke the exception chain
moved piece of code written for this to the correct new place
be tolorant of form with no top-level xmlns set