def capture(&block)
      @streams.push(@builder.target = Stream.new)
      @builder.level += 1
      str = instance_eval(&block)
      str = @streams.last.join if @streams.last.any?
      @streams.pop
      @builder.level -= 1
      @builder.target = @streams.last
      str
    end
def capture(&block)
      @streams.push(@builder.target = Stream.new)
      @builder.level += 1
      str = instance_eval(&block)
      str = @streams.last.join if @streams.last.any?
      @streams.pop
      @builder.level -= 1
      @builder.target = @streams.last
      str
    end
Captures the HTML code built inside the +block+.  This is done by creating a new
 stream for the builder object, running the block and passing back its stream as a string.

   >> Markaby::Builder.new.capture { h1 "TEST"; h2 "CAPTURE ME" }
   => "<h1>TEST</h1><h2>CAPTURE ME</h2>"