class DirectoryWatcher

DirectoryWatcher transmits messages from a filesystem server

about events happening in the filesystem. Clients can register

new watchers using the `Directory.Watch` method, where they can

filter which events they want to receive notifications for.

The DirectoryWatcher will send messages of the form:

```

struct {

uint8 event;

uint8 len;

char name[];

};

```

Where names are NOT null-terminated. The name is the relative

path to the entry the event is refering to. It will be empty if

the event isn't referencing a particular entry (e.g. for the

`IDLE` event).