Construct from a string.
authority_view( string_view s);
This function attempts to construct an authority from the string
s, which must be a valid ['authority]
or else an exception is thrown. Upon successful construction, the view
refers to the characters in the buffer pointed to by
Ownership is not transferred; The caller is responsible for ensuring
that the lifetime of the buffer extends until the view is destroyed.
authority = [ userinfo "@" ] host [ ":" port ] userinfo = user [ ":" [ password ] ] user = *( unreserved / pct-encoded / sub-delims ) password = *( unreserved / pct-encoded / sub-delims / ":" ) host = IP-literal / IPv4address / reg-name port = *DIGIT