add 204 No Content to isRedirect

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Add `No Content` to `isRedirect` method. Add tests for 201 and 204.
See also http://stackoverflow.com/questions/2342579/http-status-code-for-update-and-delete