Compatibility with http2 >= 3

[akshaymankar]

http2-3.0.0 introduced a module named Network.HTT2.Client, which implements some of the same features as this library. Given http2 is a dependency of this library, I think it makes sense to re-orient some of the features provided here to align with the way the http2 library has implemented them and get rid of the module name collision. Maybe it might also make sense to find the differences and upstream them into http2 and mark this library as deprecated.

[ProofOfKeags]

While this is ideal. The client code in http2 has a very different API than in this library as best I can tell. I would love to get there, but the documentation around the http2 client code is fairly thin, and the types are something I haven't wrapped my head around yet. It looks like the "client" in http2 is CPS encoded to accept various transport functions.