imageUploadFunction to mediaUploadFunction

First, thanks a lot for that very usefull script.

I made a small improvement that I found usefull you want to upload a file instead of just an image, so it creates a markdown link instead of an image.

Actually it works with drag & drop only, but I would find it nice to be able to add a 'Media upload' button instead of image upload for uploading pdf, doc, video, etc.

What do you think ?

#https://github.com/variablebxl/easy-markdown-editor/pull/1/commits/22f7287d187a60f11a95cbc9c6b08accc0e122ae