Laser rangefinder

This adds support for the Lightware SF0x series (tested with the SF02/F part). Its a pretty simple driver, due to the use of the HP work queue it should be fairly efficient at runtime and lightweight (in terms of stack usage).

Tested on the bench, logging works.

![laser_sf02_f](https://f.cloud.github.com/assets/1208119/2383813/39adb284-a903-11e3-9a9a-3a95ec8d00ab.png)