Some clarifications in the docstring
PUT should not return 404 when object doesn't exist

For PUT, the referenced object not existing is not an exceptional
situation, but rather expected.  It should try create the object in that
case instead of returning 404.

Of course, creating a tag under a specified id when reserving tag ids is
not yet implemented is likely to fail anyway.
Bugfix in SIngleTagAPI.put()
Merge pull request #97 from guidow/tag_api_fixes

Tag api fixes