Add cmd/fsnotify (#463)

Add cmd/fsnotify (#463)

This adds a little example that can be run:

	% go run ./cmd/fsnotify **/*
	12:76:11.4710 watching; press ^C to exit
	12:76:13.6549   1 REMOVE                "cmd/fsnotify/4913"
	12:76:13.6550   2 RENAME                "cmd/fsnotify/main.go"
	12:76:13.6550   3 RENAME                "cmd/fsnotify/main.go"
	12:76:13.6612   4 CREATE                "cmd/fsnotify/main.go"
	12:76:13.6612   5 WRITE      (modified) "cmd/fsnotify/main.go"
	12:76:13.6614   6 WRITE      (modified) "cmd/fsnotify/main.go"
	12:76:13.6648   7 CHMOD                 "cmd/fsnotify/main.go"
	12:76:15.2919   8 CREATE                "cmd/fsnotify/4913"
	12:76:15.2919   9 REMOVE                "cmd/fsnotify/4913"
	12:76:15.2922  10 CHMOD                 "cmd/fsnotify/main.go"
	12:76:15.2923  11 REMOVE                "cmd/fsnotify/main.go"
	12:76:15.2925  12 RENAME                "cmd/fsnotify/main.go"
	12:76:15.2986  13 CREATE                "cmd/fsnotify/main.go"
	12:76:15.2986  14 WRITE      (modified) "cmd/fsnotify/main.go"
	12:76:15.2988  15 WRITE      (modified) "cmd/fsnotify/main.go"
	12:76:15.3024  16 CHMOD                 "cmd/fsnotify/main.go"
	^C

It's mostly the same as the example in the README, except that it takes
paths from the commandline and aligns things a bit nicer.

This is useful for documentation and experimentation. For example, while
reviewing some PRs I found it useful to quickly get an overview of "what
does fsnotify do now, and what does it do with this patch?"