LSM303DLHC Sensor Driver

[Kevin Townsend <ke...@adafruit.com>]

I made a first pass at a driver for the LSM303DLHC using the new sensor 
API. This sensor was chosen since it has multiple sensors in a single IC 
so it can be used to test the multiple data type functionality in the 
sensor API. The magnetometer and accelerometer can also be combined 
later to generate basic orientation data to test BG processing of sensor 
data streams with useful output over the air. A simple step detection 
algorithm can also be implemented based solely on streaming accel data 
to an appropriate algorithm.

The pull request is available here along with some basic notes on using 
it: https://github.com/apache/incubator-mynewt-core/pull/147

Feel free to modify anything, this is just an attempt to get things 
moving with real HW (although having a simulated accelerometer is also 
very useful for testing purposes).

The current driver implements statistics and logging (configurable via 
syscfg.yml flags). For statistics, the sensor reads are tracked for each 
range settings for the accelerometer since the final driver will 
probably implement an auto ranging system, and it is helpful to evaluate 
the ranging system via statistics.

The magnetometer and temperature sensor will be added as the sensor API 
stabilizes, but these are easy additions.

Kevin