Making use of the new algorithmic optimisations available in Zexe (soon to be arkworks)

[jon-chuang]

The improvements will soon be merged with arkworks.

In the meantime, a description of these improvements, which will help setup time by 3-4x, are available in: https://github.com/celo-org/zexe/pull/17 https://github.com/arkworks-rs/snark/pull/296 https://github.com/celo-org/zexe/pull/26 https://hackmd.io/@celo/S10UeWUBD

The improvements have also been merged into snark-setup. The CUDA scalar mul may be incorporated into snark-setup soon enough.