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?
The geographic coordinates are assumed to be **geodetic** by default. To use geocentric or reduced latitude in spherical CS I need to calculate it from the geographic/geodetic latitude.

(http://en.wikipedia.org/wiki/Latitude#Geodetic_and_geocentric_latitudes)
> **Geodetic latitude:** (...) This is the definition assumed when the word latitude is used without qualification. (...)

(http://en.wikipedia.org/wiki/Latitude#Geocentric_latitude)
> The **geocentric latitude** (...) The relation between the geocentric latitude (ψ) and the geodetic latitude (φ) is derived in the above references as
> [an equation]

(http://en.wikipedia.org/wiki/Great_ellipse#Introduction)
> * The ellipsoid can be stretched into a prolate ellipsoid with polar semi-axis a^2/b and then mapped radially onto the sphere; this **preserves the latitude**—the latitude on the sphere is \phi, the **geographic latitude**.

> The last method gives an easy way to generate a succession of way-points on the great ellipse connecting two known points A and B. Solve for the great circle between (\phi_1,\lambda_1) and (\phi_2,\lambda_2) and find the way-points on the great circle. **These map into way-points on the corresponding great ellipse**.