Split keys with Shamir's Scheme

Fixes issue #11

This code works fine but needs a bit of cleanup. I wanted to see if you were interested in the patch before I continued.

Still needs
* add unit test
* add translations (I don't speak Spanish or French)
* Convert whitespace indent to tabs (looks terrible right now, I know)

I added the lib secrets.js.

I also apparently had to update 2 Crypto-js functions, `Crypto.util.hexToBytes` would not properly handle hex with an odd number of digits which Shamir's algorithm can produce.  Also had to update `bytesToHex` to strip off any leading zeros because that would also throw off the combining of shares.  That broke some unit tests, so I'll have to move that fix inside the secrets.js combine function.