Ability to send Audio/Video/Image messages via URL or local file.

Thought you might want to take a look at this.

I've built on top of your work to allow audio/video/images to be sent even if they are from a URL or a local file store.

I went to a lot of trouble to try and make sure that we don't get caught out of memory trying to load/get large files from the internet using things like file_get_contents.

Hopefully, unless I've messed up, none of my functions relating to sending a media file, load the file in it's entirety into memory. This should also I hope make it fast as well.

The media folder must be writable otherwise the system will default to temporary storing any downloaded URL's in the system tmp folder.

I'm not sure where to go to check what file types can be accepted for images/video/audio, nor what is the max file size we can send to the whatsapp servers. If you know please pass it on! I've just used the ones that were there and were most likely.

Some useful test files you can try this out:
Audio: http://onj1.andrelouis.com/phonetones/unzipped/Apple-iPhone3GS/UISounds/caf/alarm.caf

Video: http://techslides.com/demos/sample-videos/small.mp4

Image: http://www.voidspace.org.uk/gallery/dilbert/dilbert_certify.gif

I'm sure plenty of things can be improved, but I hope that helps you out a little!