Clean up webmachine resource specs

* Remove use of reqdata(), which is not an exported type
* Change old-style @spec to -spec
* Create context() types where needed
* Remove some unused types
* Remove use of unknown types, replace with term() where I can't figure
  out what it would otherwise be
Merge pull request #914 from basho/feature/webmachine-specs-cleanup

Clean up webmachine resource specs

Reviewed-by: cmeiklejohn