Support introspection of http major/minor version

[midnight-wonderer]

Hi
This is the minimal patch to support http.rb.
Join the ongoing discussion here: httprb/http#639.

[bryanp]

Thanks! Can you add a test for each new method in spec/integration/parser/response_parsing/introspection_spec.rb? Here's an existing test for status_code: https://github.com/metabahn/llhttp/blob/248482d0ba3c3d09000e65b53357cbb4cd5215a2/spec/integration/parser/response_parsing/introspection_spec.rb#L54-L68

[bryanp]

Thanks for the contribution!

[midnight-wonderer]

Sorry for the lack of the following-up.
At the time, I heard that you planned for a big refactor (for ruby-ffi), so I originally intended to wait for some time.
Later I don't have spare time to look into it, so I leave it stale.

Thank you for the initiative for llhttp; Ruby needs more infra guys like you.