Feature/geographic

The purpose of this PR is to move an algorithm resolving vincenty inverse problem outside of the vincenty strategy.

The goal was to add the algorithm a way of calculating not only distance but also forward and reverse azimuths and in the same time to reuse as much code as possible. I implemented a class performing a common part of the algorithm in the ctor and allowing to calculate desired result with member functions. This way it's possible to e.g. calculate the distance and azimuth without recalculating most of the intermediate values:

    vincenty_inverse<CT> vi(lon1, lat1, lon2, lat2, spheroid);
    vi.distance();
    vi.azimuth12();

The next step is to move the vincenty and andoyer strategies out of the extensions. Since Vincenty's algorithm could be used one way or another in various strategies would it be a good idea to rename it (e.g. to `vincenty_distance`)? Or would you prefer to leave the name `vincenty` for a distance strategy and pick some suitable names for possible other strategies in the future?
I implemented it this way to access radius values for all axes in Sphere, Spheroid and Ellipsoid models in a uniform way. In particular in Spheroid B (minor axis) is a radius defined for cartesian axis Z, and A (major axis) for cartesian X and Y axes. In general, it's designed this way to allow passing a Spheroid into an algorithm handling Ellipsoids. E.g. this way it'd be possible to implement only 1 function converting points on Sphere/Spheroid/Ellipsoid to 3D cartesian space.