Add Enumerable#cycle
src/string.c RESIZE_CAPA use safe name variables
This has a possibility of naming conflicts
Enumerable#reverse_each should not rely on mruby-array-ext gem
Merge pull request #1933 from suzukaze/add-enum.cycle

Add Enumerable#cycle
Fix Enumerable#cycle; ref #1933

* add multi value support
* `each` method may not rewind the sequence so that `cycle` should save elements
Merge pull request #1934 from ksss/safe-name

src/string.c RESIZE_CAPA use safe name variables
mrb_str_pool add string capa
Merge pull request #1936 from ksss/pool-capa

mrb_str_pool add string capa