Allow for pasting of image data

I kinda wanna allow for the pasting of image-data in my script. There are a few implementations I can think of for this:

1. If this video is anything to go by, then textexpander already has some support for images. So, I'll just have to figure out how they specify images, and use that to represent the image in my yml spec.
2. I could just come up with my own format.

Ultimately, if I do come up with my own format, it should be something like %file:<path to file>% or something. <path to file> should be either a local path to the file, or it should be a web link that we can curl/wget. That way, we can allow a user's texpander snippets to still feel kinda portable (you can send them to a friend, and it'll still be meaningful).

The reason I suggest the format be %file and not %image is because ultimately, it'd be cool to allow for any kind of file type. This is possible, because of mimetype. In reality, we could always allow both syntaxes, and then just get mad when %image leads to something that's not an image.

%image and %file should be considered macros. Therefore, this issue is blocked by #5 (closed), or at least blocked until the macro system for #5 (closed) is accessible.