Update DHT22 module to work with v65

Also generally improved reliability of measurements by using the checksum and additional sanity checks. Missed and bogus readings should be a thing of the past. 

Note that this will not work with versions prior to v65.
Update DHT11 module to work with v65

Port the changes in DHT22 module to DHT11 module. 

It was found that the pulse length threshold had to be changed slightly (from .0000382 to .000035) to ensure successful differentiation of pulse lengths; this seems to be straining the Espruino's ability to tell time.
Update DHT11.md

Update to reflect the fact that the checksum is now used.
Merge pull request #82 from SpenceKonde/master

Fix DHT modules to work with v65