Add support to parse http/2 request on curb adapter

Thanks to Christoph Rieß

CurbAdapter alias code from response_code

Thanks to Christoph Rieß

Add HTTP.rb v6.0.0 compatibility to http_rb adapter

Thanks to Erik Berlin

Fix compatibility with recent async-http versions

Thanks to Mikhail Doronin

Support Addressable::URI in request patterns

Thanks to Alexey Zapparov

Return support for em_http_request

Thanks to Oleg