Use MRB_ARGS_REST() instead of ARGS_REST()

Hash#{select,select!} support return Enumerator

Add Enumerable.none?

if non block given

According to include/mruby.h,

 /* compatibility macros; will be removed */
 #define ARGS_REST()         MRB_ARGS_REST()

Add Enumerable#minmax_by

Add Enumerable#minmax

Hash#each_{key,value} support return Enumerator if non block given

if non block given

use the same error message

Remove unnecessary mrb_get_args in fiber_switch.

Float#round fix bug for infinity and nan cases

Use bool-macro instead of magic-number

Use FiberError in vm.c.

Implement Fiber#transfer.

Prevent accepting String value for mrb_get_args("i")