Add in RandomNonceBox implementation

This class implements a strategy for nonce generation and transport,
that of randomly generating 24 bytes and then prepending them to the
ciphertext.  To decrypt, the reverse operation is called.
Make docs/constants consistent for RandomNonceBox

This is mostly making sure we use same named constant, etc.
Add specs for the RandomNonceBox

Which did actually catch a very important error: The box method was
returning the plain text (!).  Otherwise, they mostly check things like
round tripping.
Try and solve the encoding errors on rbx-19

Make sure we have 8-bit zeros.
Merge pull request #24 from cryptosphere/random_nonce_box

Add in RandomNonceBox implementation