@param fn Input BAM/etc filename, to which .csi/etc will be added
@param min_shift Positive to generate CSI, or 0 to generate BAI
@return 0 if successful, or negative if an error occurred (usually -1; or
-2: opening fn failed; -3: format not indexable; -4:
failed to create and/or save the index)
@param fn Input BAM/etc filename, to which .csi/etc will be added @param min_shift Positive to generate CSI, or 0 to generate BAI @return 0 if successful, or negative if an error occurred (usually -1; or -2: opening fn failed; -3: format not indexable; -4: failed to create and/or save the index)