Support for arbitrary number of steps

[jagrosh]

As things stand right now, most lyrics sources require 2 steps, a 'search' step that attempts to find a URL to a page with the lyrics, and a 'parse' step that fetches the contents at that URL and deciphers the page into usable lyrics. One source currently precedes this with a 'token' step that fetches a token that is used for future lookups.

I have concerns about how maintainable enforcing these steps will be long-term. Additionally, there are some potential lyrics sources that don't require both search and parse steps, such as https://some-random-api.ml/lyrics . I think an ideal setup would be to support an arbitrary number of steps, with the 'result' of each step (be it a token, a URL, etc) be available to all future steps, and the final step always attempting to return valid lyrics.