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

[jimthematrix]

looks great over all! have a few minor comments only. but did have one important question on why the verifiers for the 2-sized inputs were updated

[jimthematrix]

has the circuit changed for this pattern? if so what's the change? It's not obvious from the PR since the circom file got moved (so there wasn't a comparison view)

[Chengxuan]

All tokens that has encrypted values now returns the encrypted values of all output UTXOs. 273cf81#diff-23144eb2dba1e5a2d0426bafde4a643be7543faad3ad1af139cc84065ece1df4
Before the change, the circuit only return the first UTXO and had a convention that's the receiver's UTXOs.

[jimthematrix]

aha! glad I asked about this, I somehow missed the updates to the circuits for the encryption part. see my comments below

[Chengxuan]

I've missed the Golang e2e test several times as the test results were cached despite circuit changes.

Going to disable result caching for integration test

[jimthematrix]

Looks great to me! thanks @Chengxuan for the great work on this!