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?
Same here

        CT const c3 = 3;
        CT const c4 = 4;
        CT const c6 = 6;
        CT const c16 = 16;

        CT const c_e_12 = CT(1e-12);

Alternatively, you can try if it is compilable with ttmath now. We are several years further - maybe they have changed the implementation. But take care that ttmath is still supported - it is not part of the unit tests.