seth sig / seth calldata: handle tuple types

[d-xo]

The abi parser in hevm does not currenlty support tuple types (ref).

We need to implement this to be able to handle tuple types for seth sig and seth calldata.

[cruzdanilo]

https://github.com/dapphub/dapptools/issues/820 is this issue related?

[rainbreak]

I've done this in a branch along with a bunch of other abi stuff. Will make a pr soon.