* hash.c, internal.h: support theap for small Hash.
  Introduce RHASH_ARRAY (li_table) besides st_table and small Hash
  (<=8 entries) are managed by an array data structure.
  This array data can be managed by theap.
  If st_table is needed, then converting array data to st_table data.

  For st_table using code, we prepare "stlike" APIs which accepts hash value
  and are very similar to st_ APIs.

  This work is based on the GSoC achievement
  by tacinight <tacingiht@gmail.com> and refined by ko1.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65454 b2dd03c8-39d4-4d8f-98ff-823fe69b080e