Update docs
Add seed length validation
Add a new test to verify PublicKeyAuth.GenerateKeyPair(seed)
Update to libsodium 0.4.5 & fix x64

I really hope this doesn't break mono support...
Update docs for crypto_sign_seed_keypair
Remove the nunit project file for now...

Removing this until I figure out the right way to make this portable, as
right now it'll have to point to the right assembly for the developers
platform.
Using 0.4.5 now
Update version
Add a note on GPG signing