Prepend reset

Today ansi codes are appended to target text and nothing prepended.
This causes a following problem.

```elixir
IO.puts(IO.ANSI.red_background <> "hello")  #=> bg is red
Colorful.puts("hello", :green) #=> fg is green and bg is red
```

To reset the effect, This PR prepend IO.ANSI.reset before all decoration.