Add ParamKind to json-abi {,Event}Param

[DaniPopes]

currently the type field is unparsed, while ethabi users expect a parsed ParamKind enum. This would also remove the intermediate enum between the {Simple,Complex} structs

[cjeva10]

Hi, I'm interested in working on this - do we mostly want to lift from the ethabi enum ParamType?

If so I can start working on a module to modify it to fit our existing code.

[prestwich]

This got somewhat re-imagined from when we wrote the issue. Right now, the json-abi is dependency-free, and used in sol! so it cannot depend on dyn-abi as that would cause a dep cycle

@DaniPopes can you update the issue with the current thinking?

[DaniPopes]

This is no longer planned, see #210