Initial release

Miscellaneous utility functions for the Roc language. I wrote these as an exercise to learn the language. They're not optimized in any way, but as far as I can tell they work correctly.

• Hex — convert between bytes and hex strings
• Base64 — encode and decode base64 strings
• Sha — compute SHA 256 hashes
• Hmac — HMAC-SHA 256 message authentication