Add support for tuple type for inputs and outputs

[alexgaribay]

Adds support for the tuple type defined in the ABI for inputs and outputs.

For example, here's an ABI using the tuple type:

[
  {
    "name": "foo",
    "type": "function",
    "outputs: [
      {
        "name": "",
        "type": "tuple",
        "components": [
          {
            "name": "",
            "type": "uint256"
          },
          {
            "name": "",
            "type": "uint256"
          }
        ]
      },
      {
        "name": "",
        "type": "uint256"
      }
    ],
    "inputs": []
  }
]

The output type for this function would be {:tuple, [:uint256, :unit256]}.