HTTP version support detection

Added

• Add new is_http_version_supported function which allows you to check whether support for a particular HTTP version is available at runtime. When statically linking this will be entirely dependent on your build configuration, but if you are dynamically linking to libcurl then it will vary from system to system. (#368) @sagebind

Changed

• Preallocate buffer for async JSON decoding to improve performance. (#367) @michalmuskala
• Re-enable content-length request test (#383) @sagebind
• Add minimal versions test to CI (#373) @sagebind
• Refactor test server to support writing raw response data. (#366) @sagebind

Dependency Updates

• Update test-case requirement from 1.1 to 2.0 (#376) @dependabot