Adding Placeholders.js v2.1.0

I downloaded the uncompressed script from the official [Placeholders.js Github repo][1].

The minified source was downloaded from the packaged script on: [jamesallardice.github.io/Placeholders.js/][2]

* [Placeholders.js][3]
* [Placeholders.min.js][4]

These files were taken from the v2.1.0 tag.

[1]: https://github.com/jamesallardice/Placeholders.js/
[2]: http://jamesallardice.github.io/Placeholders.js/
[3]: http://jamesallardice.github.io/Placeholders.js/assets/js/Placeholders.js
[4]: http://jamesallardice.github.io/Placeholders.js/assets/js/Placeholders.min.js