AES encrypt / decrypt using passphrase

Currently the lib requires key and iv when encrypting / decrypting with AES.
I think it would be better to provide methods that use passphrase, like crypto js:
```
var encrypted = CryptoJS.AES.encrypt("Message", "Secret Passphrase");
​
var decrypted = CryptoJS.AES.decrypt(encrypted, "Secret Passphrase");
```

Locate the library's existing AES encrypt/decrypt entry points and inspect how they currently accept a key and IV. Compare the requested passphrase-based API with the CryptoJS example in the issue, then verify that encryption and decryption round-trip using the same passphrase.

Written by the indexing model from the issue text.