ds18x20 driver, updated with alarm/resolution support

[apollo2mond]

Hi all.
I have updated the ds18x20 one wire drivers and added support for

- any resolution (12-9bit)
- read/write low/high alarm trigger, scanning for alarm
- some smaller improvements

Please have a look on the sources, use it and if you want come back with feedback/hints/ideas!
I'm also thinking about a pull request for the mpy codebase after some further testing.


thanks, dk4ug

[uCTRL]

read_temp for ds18b20 returns only integer value?