delete unused indexes __m_* masks
Merge pull request #1988 from ksss/khash-mask

delete unused indexes __m_* masks
use size_t instead of int
Merge pull request #1989 from ksss/khash-size_t

use size_t instead of int
Use bool macro KHASH_DEFINE and KHASH_DECLARE
Merge pull request #1990 from ksss/khash-bool-macro

Use bool macro KHASH_DEFINE and KHASH_DECLARE