rcswitch: add driver for 314/433MHz AM devices.

[rck]

This adds a driver for 314/433MHz AM devices. A typical use case is controlling remote controlled power sockets. As there is a wider range of protocols/devices I have access to, only a part of it (type A) is tested.

In the end this sends a series of high/low pulses with time.Sleep() in between. Timing is therefore critical. Unfortunately, as of now, all the schedulers in tinygo add too much overhead. This has to be used with "-scheduler=none". There is currently an open issue documenting that[1].

Besides the scheduler limitation switching was very reliable.

tl;tr, the whole thing in action: https://twitter.com/roland_kammerer/status/1240318507943899143?s=20

[1] https://github.com/tinygo-org/tinygo/issues/962#issuecomment-600673129

[deadprogram]

Hello @rck thank you for this contribution.

I have changed the branch to dev as mentioned in our contribution guidelines here: https://github.com/tinygo-org/drivers/blob/master/CONTRIBUTING.md#how-to-use-our-github-repository

The README has some merge conflicts that now need to be resolved, if you please.