Fix bug kh_put after kh_del report by @mirichi
Qualify argv argument of API `const`.
kh_put return value should be found index
Array#rotate
Merge pull request #2043 from ksss/khash-fix

Fix bug kh_put after kh_del report by @mirichi
Merge pull request #2044 from take-cheeze/const_argv

Qualify argv argument of API `const`.
Merge pull request #2045 from suzukaze/add-array.rotate

Array#rotate
Add Array#rotate_bang
Merge pull request #2047 from suzukaze/add-array-rotate_bang

Add Array#rotate!
retrieve values in Hash#each to handle modified keys
Delegate irep string free to mrb_gc_free_str
mrb_str_dup use sheard string instead of new string