Nested media queries breaks Respond.js support in LTE IE8

[pzula]

Hey all,
I just wanted to give you a heads up for another issue that you may run across in trying to get Respond.js working in IE8. This is probably a "will not fix" issue -- but I thought I would at least document it.

The standards state that you should be able to nest media queries, however, it seems that there isn't much browser support for this yet. So if you are nesting media queries and then expect Respond.js to render the appropriate styles in IE 8 or below, beware that it will not function :)

[ndorfin]

Trying to combine the nested queries into one query also doesn't work.

i.e.

@media (min-width:320px) {
  @media (max-width:639px) {
    ...
  }
}

is the same as:

@media (min-width:320px) and (max-width:639px) {
  ...
}

:(

[gpoole]

Support nested queries would, during development, essentially fix #148 too. The debug info would be dumped into style tags but the page would still display correctly as far as I can tell and they'd be turned off in production.

[jefflembeck]

Added to README. Thanks