Changes to verify functions

Raising versions renamed to bang methods, non-raising ones replace them
Specs for key equality and lexicographical sorting

A shared example group that should cover most of the cases for both
equality and sorting.
Implement key comparison

Closes #27

Keys (Public, Private, Signing, Verify) can now be checked for equality
and also compared lexicographically.  In addition, the check for
equality is done in constant time.  But I'm not sure if the way the
checks are done means we leak anyway.  Perhaps its best to define
equality specifically anyway...
Paranoia equality

Because I don't know quite how <=> and Comparable interact to define ==.
So err on the side of safety, by explicitly defining it
Merge pull request #28 from cryptosphere/dev/compare

Implement Key Comparison