Pre-computed signatures from tool_consumer_spec were invalid

They have been regenerated from http://oauth.googlecode.com/svn/code/javascript/example/signature.html and now make the tests pass correctly
Outcome spec was failing tests because of a mallformed xml

The precomputed xml used to validate specs were wrongly not closing
itself as : <imsx_description/>

According to xml specification: http://www.w3.org/TR/REC-xml/ elements
with empty content should close itself in the same tag.
Merge pull request #10 from brodock/signature-spec-fixes

Pre-computed signatures from tool_consumer_spec were invalid
Merge branch 'master' of https://github.com/instructure/ims-lti
New XML schema in OutcomeResponseSpec
Empty replaceResultResponse element in OutcomeResponseSpec