Implement String#each_char
Proc.allocate raises a TypeError
Implement String#chars
Reuse existing code
Fix Hash#merge! when self is frozen
Implement Hash#update
Implement Enumerable#reverse_each
Merge pull request #593 from kachick/implement-string-each_char

Implement String#each_char, String#chars
Merge pull request #602 from krekoten/proc_allocate

Proc.allocate raises a TypeError
Merge pull request #604 from kachick/hash-update

Hash#merge!, Hash#update
Merge pull request #605 from kachick/implement-enumerable-reverse_each

Implement Enumerable#reverse_each