Push method

[caiotarifa]

Usually I implement my own method called push to easier handle the initialization of this library in all calls of my app.

const imgCacheQueue = []

ImgCache.push = callback => ImgCache.ready ? callback() : imgCacheQueue.push(callback)
ImgCache.init(() => imgCacheQueue.forEach(callback => callback()))

Now, you can use it like this:

ImgCache.push(() => ImgCache.cacheFile('path/to/file.jpg'))

What do you think about putting that into the library?