feat(sol!)!: gen unit/tuple structs for call types with 0/1 param

[yash-atreya]

Motivation

Closes #880
Stacked over #883

Solution

sol! {
    function totalSupply() returns (uint256);
    function balanceOf(address) returns (uint256);
}

// Unit struct
pub struct totalSupplyCall;

// Tuple struct
pub struct balanceOfCall(pub Address); // Loses name of the param

// Previously, 
pub struct totalSupplyCall {};
pub struct balanceOfCall { owner: Address }; 

• Bindings for calls with 2 or more params left unchanged.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[mattsse]

this lgtm

pending @DaniPopes