Added 'wmode' option, fixed a few IE bugs and added check for available video.stats

The 'wmode' option was needed to fix an overlay bug happening on IE/Chrome.
The 'target.dataset' had to be changed with 'target.getAttribute('data-xxxxx')' as IE doesn't support datasets.
The check for the available video.stats was needed as some videos seem to hide that data causing the player to fail.
I also updated the readme.md file with the new option infos.