is-url-superb

Fixes #11 in a bit different way of how it was being discussed. Instead of using https://github.com/sindresorhus/prepend-http, it will first try , as usual, cause it already covers all valid cases. And only if it fails, it checks if lenient mode is enabled; if so, it checks if prepending the protocol makes the input a valid url. This way we keep the logic simple and avoid adding a dependency to the package. What do you think?