Add AES-IGE-256 support

[watzon]

So this isn't going to be useful to many people as IGE is only really used in Telegram, but I'm attempting to write an MTProto library and this is something I desperately need. Apparently IGE is a pretty simple layer on top of AES that should be easy enough to do in pure Crystal (with the bindings for normal AES) for someone who's familiar with cryptography. There are a few existing libraries that have implemented IGE in C, such as cryptg (the fork by cher-nov) and tgcrypto.

[watzon]

For reference here's how they added IGE to tiny-AES-c https://github.com/cher-nov/tiny-AES-c/blob/f8507b9f226416ba1f5d452ecaaf37a2fae982c3/aes.c#L567