int written = FWrite(APTR handle, APTR buf, int size);
Function
This function has to write the specified number of bytes from the memory
buffer specified in parameter 2 to the file handle passed in parameter 1.
It has to return the number of bytes actually written.
If your file adapter doesn't support writing to files, this function can
be a dummy stub.
This function must be implemented in a thread-safe manner.