Notify debouncer

Tiny debouncer for notify. Filters incoming events and emits only one event per timeframe per file.

Features

• crossbeam enabled by default, for crossbeam channel support.
  This may create problems used in tokio environments. See #380.
  Use something like the following to disable it.

notify-debouncer-mini = { version = "*", default-features = false }

This also passes through to notify as crossbeam-channel feature.

• serde for serde support of event types, off by default