Alternative point latitude/longitude calculation from base point, bearing and distance

There is a function `vincenty` in `ol.Ellipsoid` that calculates initial bearing, final bearing and distance for given 2 latitude/longitude pairs. However, there was no function that can calculate alternative point from base point, initial bearing and distance. 

This branch contains a function called `vincentyPoint`, newly implemented in `ol.Ellipsoid`, which calculates where the alternative point is. Also, there is an example which shows the shortest path between London and Beijing, calculated by this function.

![vincenty_padding](https://f.cloud.github.com/assets/589860/982558/f829a7d8-0802-11e3-846a-96ddd7a09341.png)