Added Open VSX VS Code extension registry.
Unfortunately it currently only intersects
with Nix repository, so we encourage all repositories to use compatible and unambiguous naming scheme for vscode extensions, which
contains dot-separated namespace and extension name, for instance vscode-ms-python.flake8.
IPv6 is now treated as primary protocol for link checking: IPv4 check is now skipped if IPv6 check succeeds. The way link check status is displayed is now more verbose and readable. For the record, more than 51% links (including upstream homepages and downloads, package pages, repositories and recipes) known to Repology already support IPv6.