Add specs for Enumerable#chunk when block returns a reserved value
Fix Enumerable#chunk for a reserved symbol
Fix typo in an exception message for Enumerable#chunk
Add specs for Enumerator#peek_values
Write specs for Enumerator#next_values
Implement Enumerator#next_values
Tag failing specs
Merge pull request #2307 from kachick/enumerator-peek,next_values

Enumerator#peek_values, Enumerator#next_values
Merge pull request #2305 from kachick/fix-enumerable-chunk

Replace a reserved Symbol :_alone instead of :_singleton for Enumerable#chunk
Add benchmark for Kernel#respond_to?
Remove unused static variable
Add tags for specs in 2.0 mode