Add Helen's EndCoordinates function to MODISTools

`EndCoordinates` is a function written by Helen Phillips to calculate a set of new locations, a given distance and angle from given locations, providing start and end points of transects that can be used to extract transects of MODIS data, using `MODISTransects`.

Helen's addition to `MODISTools` comes complete with an example dataset for `EndCoordinates` and help files, both for the function and the example.