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)!
let result = SecRandomCopyBytes(kSecRandomDefault, 64,
UnsafeMutablePointer<UInt8>(keyData.mutableBytes))

db.key(keyData)

[stephencelis]

Thanks for the pull request! A few small things and I'd love to merge this.

• I've been trying to segregate Foundation code wherever possible to keep SQLite.swift as portable as possible (especially since Swift will be on Linux in the future, but Foundation may not be). Any chance you can use SQLite.Blob, instead?
• Would you please maintain the whitespace of the original file? It looks like your lines use tabs, but the rest of the project uses 4 spaces.
• Would you write a quick couple tests for the cipher target? They should basically match the other two tests.

[stephencelis]

@agisboye Any update here? If you don't want to make the changes I'll try to implement them when I have the chance.

[agisboye]

@stephencelis Sorry for the delay. I've switched to SQLite.Blob and fixed the whitespace. I haven't gotten around to the tests yet I'm afraid.

[stephencelis]

Looking good! Let me know if you need any direction getting some tests written!

[stephencelis]

Any chance we can get rid of this convenience initializer? The swift-2 branch actually uses a fully Swift implementation of Blob (no reliance on Foundation/NSData), which I may back-port, at which point you can still create a blob from NSData like this:

// data: NSData
let blob = Blob(bytes: data.bytes, length: data.length)

[stephencelis]

Any update here? Would love to merge this if you have time to add some tests!

[agisboye]

I've added tests, but I had to submit a new pull request (#317). Go ahead and remove this PR (#172).

[stephencelis]

Closing in favor of #317.