Support for DELETE method and non-200 responses

The Delete method adds support for DELETE requests.  Pretty basic.

There is a new option that can be set when issuing API calls.  Some API
endpoints return non-200 results when they succeed; for example, API
calls which do not return a response are allowed to respond with a 204
result code.  To support this without thinking it's an error, the
OkCodes field may now be initialized with a slice of valid response
codes.  If none is provided or specified, the default behavior is to
assume only a 200 response to be valid.
Merge pull request #2 from racker/delete-method

Support for DELETE method and non-200 responses
Added debugging option to print JSON request bodies
Merge branch 'working'

This merge still isn't complete because I accidentally selected the
wrong block of code in api.go, but git won't let me reset my head due to
uncommitted changes.  So, that's what this commit is for -- committing
changes, so I can fix my error.

Conflicts:
	api.go