lsm303: fix types returned by module and heading formula

* getRawAccelData() & other accel functions now return int16_t
* scale is now a supported constructor parameter
* heading returns 0-360 values

Signed-off-by: Mccool, Michael <michael.mccool@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>