Release v0.2.0 version.

This version implements:

• Extra operations needed for FieldElement and Scalar as mod_sqrt or mod_pow.

• Usage of Twisted Edwards Extended Coordinates operations. #33

• Usage of Twisted Edwards Projective Coordinates operations. #56

• Usage of Twisted Edwards Affine Coordinates for point comparison. #66

• Implementation of Compressed points which compress the sign of the x-coordinate of an EdwardsPoint. #69 #30

• Implement Point generation from a Y coordinate of the curve. #57

• Implement Random Point generation over Doppio. #51

• Docs and examples for all of the implemented modules. #52 #54 #70 #72