Calls the given block with each successive character from +self+;
returns +self+:

  'hello'.each_char {|char| print char, ' ' }
  print "\n"
  'тест'.each_char {|char| print char, ' ' }
  print "\n"
  'こんにちは'.each_char {|char| print char, ' ' }
  print "\n"

Output:

  h e l l o
  т е с т
  こ ん に ち は

Returns an enumerator if no block is given.
