Added Unsplash plugin

I've made a plugin that brings brings beautiful images from [Unsplash](http://unsplash.com)
to Sublime Text, your favorite code editor.

### Features
* Get random image (or image url) from [Unsplash](http://unsplash.com)
* Insert an `img` tag
* Insert image URL
* Insert Background Image CSS `background-image`

### How to use
* Launch the Command Palette `Shift`+`Cmd`+ P and search for Unsplash

### Keyboard shortcuts:

* `Alt` + `S` → Insert image tag
* `Alt` + `Shift` + `S` → Insert image URL
* `Cmd` + `Alt` + `Shift` + `S` → Insert Background Image CSS