Generate Bulletproofs(+) generators at compile time

Creates a new monero-generators crate so the monero crate can run the 
code in question at build time.

Saves several seconds from running the tests.

Closes https://github.com/serai-dex/serai/issues/101.

coins/monero/src/ringct/bulletproofs/mod.rs

@@ -43,14 +43,6 @@ impl Bulletproofs {
     len + clawback
   }
 
-  pub fn init(plus: bool) {
-    if !plus {
-      OriginalStruct::init();
-    } else {
-      PlusStruct::init();
-    }
-  }
-
   pub fn prove<R: RngCore + CryptoRng>(
     rng: &mut R,
     outputs: &[Commitment],