GeoJSON speed measure

This is build for surflog.app.

Given GeoJSON it will measure:

• topspeed: Fastest speed
• topspeed250: Fastest speed over 250 meter
• topspeed500: Fastest speed over 500 meter

ToDo:

• legs: Number of rides forth and back
• planing: Time planing in % (> 18 km/h)

For each position, a timestamp property is expected in order to calculate speed between each position.