unreleased-message not in old versions.

[jklymak]

In #49 we added banner at the top of all the old html pages that is

but there is no CSS for that tag before 2.0.2 and older. Need to add the following to _static/mpl.css

/* "Go to released version" message. */
#unreleased-message {
  background: #d62728;
  box-sizing: border-box;
  color: #fff;
  font-weight: bold;
  left: 0;
  min-height: 3em;
  padding: 0.7em;
  position: fixed;
  top: 0;
  width: 100%;
  z-index: 10000;
}

#unreleased-message + div {
  margin-top: 3em;
}

#unreleased-message a {
  color: #fff;
  text-decoration:underline;

}