add --help option to mruby-config

delete khash member upper_bound

Fix build fail for 'make test' with no mrbgems

Support :T_FIBER in ObjectSpace.count_objects .

test fails when we don't have Enumerator.

Delete member mask and inc

because there can be substituted by n_buckets

Use bool macro KHASH_DEFINE and KHASH_DECLARE

use size_t instead of int

delete unused indexes __m_* masks