Update `power.deep_sleep` to sleep until the next `run_every`

[microbit-carlos]

As discussed elsewhere, my suggestion is that run_every=True does not end the deep_sleep() call, but rather wakes briefly to execute the run every and then resumes the deep sleep. The deep sleep only ends when the given timeout expires, or a wake_on event occurs. In particular, power.deep_sleep(run_every=True) will never return. (And maybe we can then make run_every=True the default.)

Originally posted by @dpgeorge in bbcmicrobit/micropython#754 (comment)

[microbit-carlos]

• docs: Update Power Mgm to change run_every behaviour. bbcmicrobit/micropython#769

[dpgeorge]

Implemented by cd8bbb8