Merge pull request #49 from ebu/add-error-info

Added error_description field to error responses
Added some detail to README.md
Merge pull request #50 from ebu/pairing_code_expiry

Pairing code expiry
Changed log message on server start-up
Change 'user_code_expired' error to 'expired', to align with spec
Return JSON object with 202 response from /token
Reordered test cases
Refactored to use verifyError and sendInvalidRequest methods
Check /register response is a JSON object
Merge branch 'develop' into refactoring