module Hashie::Extensions::StringifyKeys

test # => {'abc' => 'def'}
test.stringify_keys!
test = {:abc => 'def'}
@example

Convert all keys in the hash to strings.

def stringify_keys!
  keys.each do |k|
    stringify_keys_recursively!(self[k])
    self[k.to_s] = delete(k)
  end
  self
end