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 someting like the following to disable it. toml 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