Implement Bulletproofs in Rust (#69)

* Initial attempt at Bulletproofs

I don't know why this doesn't work. The generators and hash_cache lines
up without issue. AFAICT, the inner product proof is valid as well, as
are all included formulas.

* Add yinvpow asserts

* Clean code

* Correct bad imports

* Fix the definition of TWO_N

Bulletproofs work now :D

* Tidy up a bit

* fmt + clippy

* Compile a variety of XMR dependencies with optimizations, even under dev

The Rust bulletproof implementation is 8% slower than C right now, under 
release. This is acceptable, even if suboptimal. Under debug, they take 
a quarter of a second to two seconds though, depending on the amount of 
outputs, which justifies this move.

* Remove unnecessary deref in BPs

Cargo.toml

@@ -21,6 +21,22 @@ members = [
   "contracts/multisig",
 ]
 
+# Always compile Monero (and a variety of dependencies) with optimizations due
+# to the unoptimized performance of Bulletproofs
+[profile.dev.package]
+subtle = { opt-level = 3 }
+curve25519-dalek = { opt-level = 3 }
+
+ff = { opt-level = 3 }
+group = { opt-level = 3 }
+
+crypto-bigint = { opt-level = 3 }
+dalek-ff-group = { opt-level = 3 }
+
+multiexp = { opt-level = 3 }
+
+monero-serai = { opt-level = 3 }
+
 [profile.release]
 panic = "unwind"