Hash-based VDFs, MIMC and STARKs

I streamlined the Go STARK implementation with goroutines, channels + big.Int optimizations and on an ordinary laptop (2014 MacBook Pro 2.2 GHz Intel Core i7 with 8 “logical” cores) got to this basic level of temporal performance:

NUM_CORES STARK Proof Generation STARK Verification
1 3.12s 46.11ms
2 2.01s 24.70ms
4 1.49s 15.64ms
8 1.42s 16.58ms
16 1.49s 18.30ms
32 1.48s 20.18ms
ethereum/research python 3.78s 52.10ms