envflag.go
func BoolVar(p *bool, name string, value bool, usage string) {
	EnvironmentFlags.BoolVar(p, name, value, usage)
}
func BoolVar(p *bool, name string, value bool, usage string) {
	EnvironmentFlags.BoolVar(p, name, value, usage)
}
// BoolVar defines a bool flag with specified name, default value, and
// usage string.  The argument p points to a bool variable in which to
// store the value of the flag.