ev3dev.1.0.0-compatible motor api

There was a major rewrite of the motor drivers in version 1.0.0 of ev3dev. Therefore the motor API needs to be updated. In this branch I've made some backwards-compatible changes to meet this requirement.

Actually I am new to Golang so you are welcome to suggest any improvements/fixes.

Moreover the docs should probably be updated to point users on the correct version of GoEV3 depending on ev3dev's version they use.