Implement Hash#key
alphabetize
Fix compilation of certain regexps
Implement Hash#index

TODO comment format is ported from Array#initialize
use is when comparign with None
Kernel#=== should check identity

Kernel#=== for a class with #== and #equal? overridden to always be false returns true if the object id is the same even if both #== and #equal? return false
Merge pull request #592 from kachick/implement-hash-key

Implement Hash#key, Hash#index
Merge pull request #596 from krekoten/kernel_case_compare

Kernel#=== should check identity
Implement String#concat
Merge pull request #597 from kachick/implement-string-concat

Implement String#concat
sort tags
Merge pull request #598 from kostya/sort

sort tags