Allow multiple exensions to be assigned to File ops modules

File ops modules that read/write kaze objects currently can only be assigned one file extension to read/write from, in KFileOps.extension .

Because some readers may be able to handle multiple file extension types, it would make sense to allow multiple exensions to be registered to a single file ops module, using a comma-separated list.

example:

static KFileOps vid_fops = {
    .extension = "avi,mkv,mp4,m4v,mpg,mp2,mpeg,mpe,mpv,m2v,mov",
    .reader = vid_fops,
    .writer = vid_fops
};

In addition, extensions should NOT be case-sensitive. Currently the file extensions have to match case exactly in order to be loaded.