SDI12 Datalogger Loom Integration

[WL-Richards]

We should have the option for Loom to act as a datalogger, responding to SDI12 requests. Here is the example from the SDI12 library for responding to requests: https://github.com/EnviroDIY/Arduino-SDI-12/blob/master/examples/h_SDI-12_slave_implementation/h_SDI-12_slave_implementation.ino

[udellc]

Loom to relay all sensor data out on an SDI12 bus, something like log.SDI12 would be cool. Need to wait for measure request from master SDI12 device. And accompanying example for setting up a Loom device in SDI12 slave mode.