Add method to convert specimen position object to list.
Allow negative index in get_position(...).
Support calculate of position if end position is specified.
Remove restriction on z being equal, use average z.
Fix bug in operation of specimen position when there are different
units.
Fix problem of get_index when explicit calibration is not sorted.
Add get_index method to retrieve index from position.
Remove unused module.
Add stitch function to stitch different image raster data if enough
information is given in the conditions.