Add the ability to add a copyright

Signed-off-by: Peter Olds <polds@kyanicorp.com>

app.go

@@ -43,6 +43,8 @@ type App struct {
 	Compiled time.Time
 	// List of all authors who contributed
 	Authors []Author
+	// Copyright of the binary if any
+	Copyright string
 	// Name of Author (Note: Use App.Authors, this is deprecated)
 	Author string
 	// Email of Author (Note: Use App.Authors, this is deprecated)

help.go

@@ -28,7 +28,10 @@ COMMANDS:
    {{end}}{{if .Flags}}
 GLOBAL OPTIONS:
    {{range .Flags}}{{.}}
-   {{end}}{{end}}
+   {{end}}{{end}}{{if .Copyright }}
+COPYRIGHT:
+   {{.Copyright}}{{end}}
+
 `
 
 // The text template for the command help topic.