add initial crypto algorithms

This library implements multiple secret-sharing algorithms
which will be used by the archistar secure multi-cloud
prototype. Focus is foremost on readability.

Implemented directives include:

 * shamir secret-sharing
 * rabin IDS
 * krawczyk "secret sharing made short"
 * rabin-ben-ora verifiable secret sharing

Archistar was originally created in 2013 at the Austrian
Insititute of Technology (http://www.ait.ac.at), Vienna,
Austria by Franca-Sofia Fehrenbach under supervision of
Thomas Loruenser.

This commit is based on heavily-refactored code by Andreas
Happe and Thomas Loruenser, all bugs will be due to this
refactoring.