v0.5.0

Add garbage collection on buckets:

• #32
• #33

Two methods:

• GC(), which scans all buckets and deletes those that are no longer valuable. Our definition of “valuable” is “full” — containing as many tokens as specified in its Limit. A full bucket contains no useful state, and is semantically identical to no bucket; new buckets are created full.
• Clear(), which simply drops all buckets regardless of state. You might call this during a low traffic period.

We don’t run GC on your behalf, but offer it as a primitive that you can call on a schedule of your choosing. We’ll likely add more observability so users can know how much garbage there is.

Full Changelog: v0.4.0...v0.5.0