Instead of imposing the requirement that bellman users explicitly
specify an engine for every proving system, we allow the Rust type
system to figure it out for us. An engine is specifically useful in
places where we require defined relationships between several types;
ff::ScalarEngine only has one type, and thus any usage of it can be
trivially replaced by an explicit Scalar type. This is also more
readable :)
The ff_derive, pairing, zcash_primitives::jubjub, and bellman dummy_engine
changes are minimally implemented on top of the existing *_assign()
functions.
Jack Grigg
Eirik Ogilvie-Wigley