Includes better support for iframes using a prop that can be used to determine which window to use (see #78).

This release adds a <Media targetWindow> prop that can be used to determine which window to use (see #78).

Uses "development" mode in the dev UMD build.

This release adds the <Media defaultMatches> prop that should help people doing SSR (see #46 for discussion).

It also uses the prop-types package instead of React.PropTypes which is deprecated in React version 15.5.