Support human-redeable ABI format in ContractCondition.functionAbi

[piotr-roslaniec]

• Support function signatures of the form myFunction(address, uint256):uint256 in addition to JSON ABI format
• Provides less verbose functionAbi interface

[cygnusv]

I've sometimes seen this notation myFunction(address, uint256):(uint256, bool) that allows you to specify multiple output types

[piotr-roslaniec]

ethers refers to this notation as Human-Readable ABI format

[derekpierre]

Note that any addition here that is different from the JSON ABI format will need an associated change in nucypher for the nodes to appropriately handle it.