Replace Executor with Reloader

Put value from synchronous loading to cache directly

Align fields for atomic access on 32-bit

Add write queue to refresh/expiry entries by write time

Add Ristretto cachebench

Combine event channels

Make use of multiple cache segments

Replace Travis with GitHub Actions

Use sync.Map and atomic.Value to reduce lock contention

Add go.mod

Bump go version

Add ExpireAfterWrite

Update example

Merge pull request #5 from goburrow/races

Fix races on closing cache