Move the KlippyConnection class into its own module. Refactor
init to use loops rather than callbacks, this reduces complexity
of tracking and cancelling callback handles.
All Klippy state previously tracked by the Server is now in the
KlippyConnection. This improves testing and makes the code
less ambiguous, ie: the `server.make_request()` method is not
as clear as `klippy.request()`.
Signed-off-by: Eric Callahan <arksine.code@gmail.com>
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