Add support for recircluation pump control

[TwoClocks]

Newer Rheem tankless heaters have a recirculation pump that's controllable from the app.

The main command to run the pump is:
"@RPUMPINSTANCE" which turns on the pump, and looked like this:

{'constraints': {'enumText': ['Off', 'On '],
                 'enumTextIcon': [],
                 'lowerLimit': 0,
                 'upperLimit': 1},
 'status': 'Off',
 'value': 0}

There is also "@RCOPERATIONS" which returns a nice string like Recirc pump not circulating

Lastly, there is "@RPUMPMODE," which controls how often the pump runs. I think you can ignore this one.

{'constraints': {'enumText': ['None        ',
                              'Timer-Perf. ',
                              'Timer-E-Save',
                              'On-Demand   ',
                              'Schedule    '],
                 'enumTextIcon': [],
                 'lowerLimit': 0,
                 'upperLimit': 4},
 'status': 'On-Demand   ',
 'value': 3}

I verified that it works via the equipment._api.publish API in your library.

I would take a stab at a PR, but my python is rusty. Also, it's very unclear to me how/if the API deals with features that are device-dependent.

It would be great to add this to HomeAsstant. Recirculation pumps waste a lot of energy when run on timers. Being able to control them via automation to circulate before use would save energy, and still have relatively fast hot water.

[w1ll1am23]

Not sure when I'll have time to look in to this, but this is a good idea. I'll try to take a look and send you something for testing if I get anything working.