Merge pull request #1 from damiancarrillo/master

Correcting documentation surrounding length of nonces and private keys
Merge pull request #2 from damiancarrillo/master

Updating libsodium
Updating libsodium-darwing-build
Merge pull request #3 from damiancarrillo/master

Using NSSecureCoding instead of NSCoding
Merge branch 'master' of github.com:Tabbedout/SodiumObjc
Cleaning up

- Renaming secret -> private
- Fixing a poorly named method