Get numbers of zk-snarks

[boolafish]

Description

As a venue, I want to know what's the limit of using zk-snark, So that I knows how many orders I can put into per batch settlement.

As a OMG network provider, I want to know what's the speed to generate zk-snark, So that I can make decision on whether we can use this technology and know what is expected TPS when using this technology.

sub story of #53 ref #76

Successful Criteria

• Get time metric on generating proof. (As we don't have a fixed solution yet, probably run several proof on different computation complexity and get a good metric in general?)
• Get gas cost metric on verifying zk-snark on chain.

[boolafish]

numbers in the file linked in readme of this repo: https://github.com/omisego/snark-playground