Make the scale factor of ol.format.Polyline configurable

The default scale factor is `1e5` (see [Google algorithm](https://developers.google.com/maps/documentation/utilities/polylinealgorithm))

OSRM returns a polyline scale with a `1e6` factor.

Ping @Turbo87
`encodeDeltas`, `encodeFloats`, `decodeDeltas` and `decodeFloats` are now exported