Apsg

* FaultSet class added. Fault and Hoeppner methods of StereoNet implemented
* VelGrad and DefGrad classes used for transformations added
* G class to quickly create groups from strings added.

* Quick plotting of groups fixed.

* new StereoNet class for Schmidt projection
* Quick plot when data are passed as argument `StereoNet` class instantiation
* mplstereonet dependency depreceated
* new `Pair` and `Fault` classes to manipulate paired data (full support in future)
* new `uniform_lin` and `uniform_fol` `Group` methods
* abs for `Group` implemented to calculate euclidean norms
* new `Group` method normalized
* new `Group` properties and methods to calculate spherical statistics

* First release of APSG