Multiple laps

[stela]

Handle waypoints wraparound and override any zero speed waypoint provided.

[stela]

Intended to resolve #7.

[StefanGerlach]

Works well!

[stela]

We should probably reverse part of this change if we need to re-submit, apparently the car is supposed to respect the 0 waypoint speeds, see https://carnd.slack.com/archives/C6NVDVAQ3/p1522261806000786

Stephen Welch
Hi All! The vehicle should follow the speed set for each waypoint (in this case coming to a stop at the end of the waypoints). We don't expect the vehicle to be able to continuously drive in a loop. However, we may try to restart the dbw in the middle of the waypoint set after driving the loop once, if needed. (e.g. if we want to get another shot at the traffic light.)

From a thread in #s-t3-p-system-integra, Mar 28th at 20:30

The wraparound-support though seems useful, should keep that part, just remove the waypoint speed change.