templates/templates.go
func WithFileFindFunc(fn func(filename string) string) Option {
	return func(o *Options) { o.fileFindFunc = fn }
}
func WithFileFindFunc(fn func(filename string) string) Option {
	return func(o *Options) { o.fileFindFunc = fn }
}
// WithFileFindFunc sets the function that will return the
// file path on disk based on filename provided from files
// defind using WithTemplateFromFile or WithTemplateFromFiles.