def strip_indent(s, n)
      while n > 0
        case s[0, 1]
        when ' '
          n -= 1
        when "\t"
          n -= TAB_SIZE
        else
          break
        end
        s = s[1..-1]
      end

      MDLine.new(s)
    end
def strip_indent(s, n)
      while n > 0
        case s[0, 1]
        when ' '
          n -= 1
        when "\t"
          n -= TAB_SIZE
        else
          break
        end
        s = s[1..-1]
      end

      MDLine.new(s)
    end
Removes indentation from the beginning of `s`,
 up to at most `n` spaces.
 Tabs are counted as {TAB_SIZE} spaces.

 @param s [String]
 @param n [Fixnum]
 @return [String]