matchers.go
func NewPathPrefix(prefix string) PathPrefix {
	if !strings.HasPrefix(prefix, "/") {
		prefix = "/" + prefix
	}
	return PathPrefix(prefix)
}
func NewPathPrefix(prefix string) PathPrefix {
	if !strings.HasPrefix(prefix, "/") {
		prefix = "/" + prefix
	}
	return PathPrefix(prefix)
}
// PathPrefix -----------------------------------------------------------------
// NewPathPrefix returns a static URL path prefix matcher.