Rewriting code to use airbreathercore.

- No functional changes in 2.0.1, so if you already have 2.0.0, then
don't bother updating.
- Most of the really cool code moved out of YALSM and into
airbreathercore, so updating this code to use that instead of the
original versions.
- Removing dead code that's not needed (yet?)
- Updating the instructions in the README.
- Importing airbreathercore as a submodule.