These drivers can now be used by any port (so long as that port has the
_onewire driver from extmod/modonewire.c).
These drivers replace the existing 1-wire and DS18X20 drivers in the
drivers/onewire directory. The existing ones were pyboard-specific and
not very efficient nor minimal (although the 1-wire driver was written in
pure Python it only worked at large enough CPU frequency).
This commit brings backwards incompatible API changes to the existing
1-wire drivers. User code should be converted to use the new drivers, or
check out the old version of the code and keep a local copy (it should
continue to work unchanged).