Giving multidict Cython Or PyCapsule Support?

[Vizonex]

I feel very tempted to ask if I could make it so that Cython could actually support multidict rather than just simply importing it since I feel that performance may steadily improve if this approach was implemented. This way instead of calling import multidict we could do something like cimport multidict I would assume that doing so would allow the following things in aiohttp to run a bit faster.

• The _http_writer.pyx Cython Code could have direct access to istr as a physical CPython Type allowing this check to be a little bit smoother.
• As for _http_parser.pyx this could be pretty significant as many of the multidict calls could be replaced for C-API Calls.

Approach For Compiling

• As for compiling I'm looking to try and approach this the same way numpy would where a call like _import_array() could be implemented to import the Capsule.
• There could be an extra module that is specifically responsible for finding the header files at compile-time so that users who want to use multidict within cython can easily compile their code alongside with it.

If anybody is confused about what a capsule is I have a link to it's documentation

[webknjaz]

As long as the pure-python implementation remains functional, this might be reasonable to explore, I suppose. Although, I think @bdraco mentioned compatibility difficulties with cross-project cython imports at some point.