Crypto

This is a preliminary submission to add support for encrypting Python bytecode using PyCrypto's AES
block cipher module.

This shouldn't be merged just yet since I have to write tests, and I might have overlooked some detail
(especially on the crypto side of things).

It is mostly working, but it requires PyCrypto 2.4. Newer versions of PyCrypto have changed in structure, which
turns bundling the AES module into a difficult affair.