Allow checking HTTP version support at runtime

[sagebind]

Add is_http_version_supported which allows you to check which HTTP versions are supported by a particular build of Isahc at runtime. This could be used to decide whether an application would choose to enforce HTTP/2 for example, or just to verify that build configuration is as expected.

[codecov]

Codecov Report

Merging #368 (26c6936) into master (f3b5c3c) will increase coverage by 0.14%.
The diff coverage is 80.64%.

@@            Coverage Diff             @@
##           master     #368      +/-   ##
==========================================
+ Coverage   79.34%   79.48%   +0.14%     
==========================================
  Files          51       52       +1     
  Lines        3060     3086      +26     
==========================================
+ Hits         2428     2453      +25     
- Misses        632      633       +1     

Impacted Files	Coverage Δ
src/lib.rs	76.19% <ø> (+14.65%)	⬆️
src/info.rs	80.64% <80.64%> (ø)

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