templates/templates.go
func WithFunctions(fns template.FuncMap) Option {
	return func(o *Options) {
		for name, fn := range fns {
			o.functions[name] = fn
		}
	}
}
func WithFunctions(fns template.FuncMap) Option {
	return func(o *Options) {
		for name, fn := range fns {
			o.functions[name] = fn
		}
	}
}
// WithFunctions adds function map to templates.