Consider removing support for proc_macro::TokenStream and only support proc_macro2::TokenStream #17
Description
Due to dtolnay's decision in dtolnay/quote#89 it is unlikely we will get support for ToTokens and Parse for the proc_macro types.
While so far I've been able to work around this with macro magic, this makes the code a lot harder to maintain due to not being able to move more complex type logic into traits / normal generics instead of macros.