asio: Add support for static build + Windows dynamic MSVC

[vserdyuk]

This adds support for:

• building dynamic nghttp2_asio with MSVC
• building static nghttp2_asio (checked on macOS and Linux)

It still needs getopt.h. I use a getopt-win32 implementation from vcpkg repo, but it needs a patch.

I've made a demo project which uses vcpkg with my patches for nghttp2_asio, getopt-win32 and vcpkg itself: https://github.com/vserdyuk/nghttp2_asio_test

Hope to get all of this upstreamed so others can get nghttp2_asio via vcpkg easily without patching.

Related issues:

• https://github.com/nghttp2/nghttp2/issues/933
• https://github.com/nghttp2/nghttp2/issues/589

[vserdyuk]

Please, kindly review this PR. I will try to resolve issues, if any.

[tatsuhiro-t]

Closed since asio library has been removed.