matchers.go
func NewScheme(m []string) Scheme {
	for k, v := range m {
		m[k] = strings.ToLower(v)
	}
	return Scheme(m)
}
func NewScheme(m []string) Scheme {
	for k, v := range m {
		m[k] = strings.ToLower(v)
	}
	return Scheme(m)
}
// Scheme ---------------------------------------------------------------------
// NewScheme retuns a URL scheme matcher, converting values to lower-case.