Loads a new bitmap into the snip.
Loads the file by passing filename and flags to load-file If a bitmap had previously been specified with set-bitmap, that bitmap will no longer be used. If filename is null, then the current image is cleared.
If relative-path? is not #f and filename is a relative path, then the file will be read using the path of the owning buffer's filename. If the image is not inlined, it will be saved as a relative pathname.
If inline? is not #f, the image data will be saved directly to the file or clipboard when the image is saved or copied. The source filename is no longer relevant.