[1.x] Support PSR-7 v2 along side v1#549

WyriHaximus wants to merge 1 commit intoreactphp:1.xreactphp/http:1.xfrom

WyriHaximus-labs:1.x-psr-7-v2WyriHaximus-labs/http:1.x-psr-7-v2Copy head branch name to clipboard