Versionate

[eloyesp]

Currently there is no way to know the version of the polyfill, it would be nice have some versioning scheme and even a changelog. Having versions in place, it would be easier to add some compatibility indicator (what browser versions this polyfil works with).

The versioning should go to git tags, but should also be added on the code itself (at least as a comment) to make it easier to check which version is in use.