Update the DLEq proof for any amount of generators

The two-generator limit wasn't required nor beneficial. This does 
theoretically optimize FROST, yet not for any current constructions. A 
follow up proof which would optimize current constructions has been 
noted in #38.

Adds explicit no_std support to the core DLEq proof.

Closes #34.

crypto/dleq/Cargo.toml

@@ -30,9 +30,10 @@ dalek-ff-group = { path = "../dalek-ff-group" }
 transcript = { package = "flexible-transcript", path = "../transcript", features = ["recommended"] }
 
 [features]
-serialize = []
-experimental = ["multiexp"]
+std = []
+serialize = ["std"]
+experimental = ["std", "multiexp"]
 secure_capacity_difference = []
 
-# Only applies to cross_group, yet is default to ensure security
+# Only applies to experimental, yet is default to ensure security
 default = ["secure_capacity_difference"]