Media Query support

Similar to CSS, media query support in UISS allows you to have layouts
specific to various device configurations (e.g.: iPhone 4 vs 5). This
code is also extensible to allow for additional properties (e.g.:
device-version: 6, device-version: 7) in the future.

Since UISS files are evaluated once at runtime, media queries can only
be used to evaluate device-specific properties.
Try the easy way out when searching for selectors

Searching for selectors is highly expensive (on our app, we spend 14.7
seconds on iPhone 3GS doing this), and we see massive performance gains
if we first try the most common pattern. With this fix, load time is
shaved by over 10 seconds.
Merge branch 'master' of https://github.com/btaylor/UISS

Conflicts:
	README.md