func (h *Hash) Delete(key Value) (*MrbValue, error) {
	keyVal := key.MrbValue(&Mrb{h.state}).value
	result := C.mrb_hash_delete_key(h.state, h.value, keyVal)
	val := newValue(h.state, result)
	if val.Type() == TypeNil {
		val = nil
	}
	return val, nil
}
Delete deletes a key from the hash, returning its existing value,
or nil if there wasn't a value.
package mruby
import "C"
type Hash struct {
	*MrbValue
}