New Async API client

[jbusecke]

I have taken what I have learned from #42 and written a completely new logic to get info from the ESGF API.
This one is a bunch simpler, not async, and seems to actually get a lot more URL information (tested with the cases in #42).

I think the design here can also accomodate leap-stc/cmip6-leap-feedstock#147 in general. It might also be relevant to leap-stc/cmip6-leap-feedstock#133 (if we want to inject dataset level tracking ids).

Ill test drive this over at the CMIP6 feedstock and will then finish up over here.

This seems to work really well so far. I had a few hangs, but after actually raising timeouts, and catching them, things seem to work fine.
Will have to finish up the things below, but am already starting to use this on the CMIP recipe.

• Decide on how to deal with Incomplete file listings #46
• Evaluate if at this point we could also use the official client? no, too slow
• Remove the recipe_input module
• Migrate the backoff/retry logic from the old async code -> Consider reimplementing the backoff/retry logic if needed  #48
• Make a loud announcement about the breaking changes
• Make sure to release a new major version after completing this.
• Loosen dependencies?