Added amd support (2 lines)
Non-root relative paths (no '/' prefix) resolve correctly, and 'back' alias added to page for consistent API access
Updates to README for addition of 'back' to API
Updated to work in IE8 + 9, when polyfilled.

Changes required:
 - bubbled click events have to bind to the body, not window
 - use attachEvent when addEventLister is not defined
 - event object can be different (e.srcElement, e.which, preventing default).
 - el.location is different
Use `history.location` before `document.location`.

Changes from @devote. We need to look at `history.location` when it exists (for polyfilled browsers, as `document.location` will included a hash.