add reference systems and coordinates transformations

[aqreed]

@jorgepiloto,

I am also working in this module (and its tests) in my fork, adding coordinates transformations (LLA to ECEF and NED to ECEF). In the near future I will add some more and also improve the idea (be able to use different geodetic models, for example).

Question is, should I open a pull request now, or better wait until the module achieves some maturity?