SQLiteCipher NSData key support

[agisboye]

Adds key and rekey methods that accept a key of type NSData.
This allows the database to be easily keyed with a key generated by
Security.framework:

let keyData = NSMutableData(length: 64)!
SecRandomCopyBytes(kSecRandomDefault, 64,
UnsafeMutablePointer<UInt8>(keyData.mutableBytes))
db.key(Blob(bytes: keyData.bytes, length: keyData.length))

[stephencelis]

Did you mean to key against keyData?

[stephencelis]

This is great! Found a small typo, but it's good to merge otherwise. @mikemee and I are in the process of extracting SQLiteCipher.swift into its own repo, so we'd like to get this in before #314 gets merged!

[agisboye]

I knew I'd missed something. Here we go. :-)

[stephencelis]

Thanks!