[WIP] carrot_core

[jeffro256]

This PR is to implement all non-"legacy" Carrot cryptography, as well as enote creation logic and enote scanning logic.

https://github.com/jeffro256/carrot/blob/master/carrot.md

• [x] Non-legacy carrot enote creation
• [x] Non-legacy carrot enote scanning
• [ ] Tests for new enotes addressed to legacy cryptonote accounts/addresses
• [ ] Transaction output set finalization logic
• [ ] Transaction scanning ease-of-use functions with ECDH reuse
• [ ] Efficient implementation for X25519 unclamped scalar multiplication and cofactor clear
• [ ] Hardware device interface
• [ ] IRL Hardware device support (although this won't go in carrot_core)