curl adds IPFS support

curl now supports IPFS URLs such as ipfs://, so users can fetch IPFS content without writing out a gateway address. curl rewrites the IPFS URL into a gateway URL, using the IPFS_GATEWAY environment variable, a ~/.ipfs/gateway file, or the --ipfs-gateway argument to find the gateway. The --ipfs-gateway argument overrides other settings and does not fall back to them if it fails. Gateway redirects are not followed by default, so the -L option is needed to follow them, such as dweb.link's redirect from path-based to subdomain-based requests.