Return true if a userinfo is present
This function returns true if this contains a userinfo.
assert( url_view( "http://jane%2Ddoe:pass@example.com" ).has_userinfo() );
userinfo = user [ ":" [ password ] ]
authority = [ userinfo "@" ] host [ ":" port ]
has_password , encoded_password , encoded_user , encoded_userinfo , password , user , userinfo .