Add HTTP API for datatypes.
Address review comments.

* Remove extraction of undefined path segment into the resource
  context.
* Guard the timeout parameter check to make sure it is greater than 0.
* Add explanatory comment about the redirection when using the default
  bucket-type.
Make 0 timeout qs param mean infinity.
Merge pull request #732 from basho/feature/sdc/crdt-http-api

Add HTTP API for datatypes.