-`dir` - The directory whose contents to watch. It's recommended, though not required, for this to be an absolute path, say one returned by `path.resolve`.
-`filter({ path, stats })` - _(optional)_ A function to decide whether a given file or directory should be watched. It's passed an object containing the file or directory's relative `path` and its `stats`. It should return `true` or `false` (or a `Promise` resolving to one of those). Returning `false` for a directory means that none of its contents will be watched.
-`watch` - _(optional)_ Whether to actually watch the directory for changes. Defaults to `true`. If `false`, you can retrieve all of the files and directories within a given directory along with their initial `Stats` but changes will not be monitored.
-`debounce` - _(optional)_ Length of timeout in milliseconds to use to debounce incoming events from `fs.watch`. Defaults to 10. Multiple events are often emitted for a single change, and events can also be emitted before `fs.stat` reports the changes. So we will wait until `debounce` milliseconds have passed since the last `fs.watch` event for a file or directory before handling it. The default of 10ms Works On My Machine.
A `Map` of the watched files and directories. Each key is a relative path from the `CheapWatch`'s `dir`, and each value is a `Stats` object for the file or directory. Paths are always separated by forward slashes, regardless of platform. This `Map` is kept up to date as files are changed on disk.
A `+` event is emitted whenever a watched file or directory is created or updated. It's emitted with an object containing a `path` string, a `stats` object, and an `isNew` boolean which will be `true` for newly created files and directories and `false` for updated ones.
A `-` event is emitted whenever a watched file or directory is deleted. It's emitted with an object containing a `path` string and a `stats` object. `stats` will be the most recent `Stats` collected for the file or directory before it was deleted.