func KeyFormatter(v KeyFormatterFunc) Option {
	return func(opts *Options) {
		if v != nil {
			opts.KeyFormatter = v
		}
	}
}
KeyFormatter sets the key formatter
default : func (keys []string) => strings.Join(keys, "#")
package tabify
import "strings"
type Options struct {
	KeyFormatter KeyFormatterFunc
	KeyExcluder  KeyExcluderFunc
}
type Option func(o *Options)
type KeyFormatterFunc func([]string) string
type KeyExcluderFunc func([]string) bool
func newOptions(opt ...Option) Options {
	opts := Options{}
	for _, o := range opt {
		o(&opts)
	}
	if opts.KeyFormatter == nil {
		KeyFormatter(defaultFormatter)(&opts)
	}
	return opts
}
func defaultFormatter(keys []string) string {
	return strings.Join(keys, "#")
}