Documentation is lacking for manually ABI-encoding structs

[nventuro]

Hi! The ABI encoder works fantastic for Solidity contracts with functions that receive structs (though error diagnosis and reporting could be better when a field is missing 😅), but I couldn't find much info in using this machinery to manually ABI-encode a struct.

The documentation doesn't provide any examples on how to do this, and while this Google-able comment shows encoding of a tuple, I couldn't find the equivalent for structs.

Given protocols are becoming more complex and configurable, and that a solution for stack-too-deep doesn't seem to be coming anytime soon, memory structs seem like the way to go for most projects, and better support for them would be extremely helpful. Thanks!

[ricmoo]

The PR for #1302 will address this, and the discussion #1301 will help too.

[ricmoo]

Added some examples.

Thanks! :)