Interface change: Added Response.Reset()

The `Response` interface now requires an additional `Reset` method.
`Run` and `RunOrPanic` will trigger this `Reset` method at the
beginning.

This will fix bug #2.
Interface change: Added Response.Reset()

The `Response` interface now requires an additional `Reset` method.
`Run` and `RunOrPanic` will trigger this `Reset` method at the
beginning.

This will fix bug #2.
Force case response to implement restit.Response

If the response does not implement restit.Response, there will either
be compile error or the test fails to run.