supports larger sized input & output utxos

[Chengxuan]

This PR propose a method for all the fungible tokens to support more than 2 inputs.

• A batch version of circom circuits has been proposed for each token examples
• The solidity contract has been updated to choose between the small (2) and large (10) input circuit depends on the input size
• Contract with encrypted values now returns encrypted values of all outputs (rather than the first one) for batching scenario
• didn't write new tests for batch version of the circuit as the core logic has already been covered by existing tests
• added -v verbose mode which prints out output of circom commands. it contains the number of constraints in the generated circuit, which is helpful for picking PTAU files
• added a test to ensure concurrent witness generation works as expected in golang SDK: golang witness generation concurrency test #87

Resolves #8