With a block given, calls the block with each successive character from +self+;
returns +self+:

  a = []
  'hello'.each_char do |char|
    a.push(char)
  end
  a # => ["h", "e", "l", "l", "o"]
  a = []
  'こんにちは'.each_char do |char|
    a.push(char)
  end
  a # => ["こ", "ん", "に", "ち", "は"]

With no block given, returns an enumerator.

Related: see {Iterating}[rdoc-ref:String@Iterating].
