Create iso9660/fat images on the fly

[copy]

This would allow sharing files with guests that don't support 9pfs. Probably depends on #54.

[cognitivegears]

So, not directly using v86, but because v86 allows you to specify a buffer instead of a url, you should be able to use another library to do the file manipulation itself. I'm still working on this myself, but I'm using the fatfs library (https://github.com/natevw/fatfs) along with a fatfs-volume-driver library I wrote (https://github.com/cognitivegears/fatfs-volume-driver) to allow a FAT volume to be manipulated prior loading into the v86 emulator. I haven't tried it yet with a browser, though as far as I'm aware it should work there as well.