Phenopype

------
bugfix:
- add_files with multiple ex- or include argument created duplicated filelists

------
- New feature: scale (former scale_maker) can now automatically equalize histograms via interpolation. Was mostly inspired by this SO question: https://stackoverflow.com/questions/32655686/histogram-matching-of-two-images-in-python-2-x
- renamed "scale_maker" method to "scale", and subfunctions, too. tutorials updated. more name changes to come towards a more intuitive naming convention
- show_img can now show multiple images when list is provided
-

------
- scale_maker is completely reworked: now has zoom and onscreen notifications for mm/pixel info. measuring scale and making a template for detection are now two separate functions (measure_scale and make_scale_template)
- documentation and API reference for tracking module added
- test for scale added

------
- landmark_maker has now (limited) mousewheel zooming functionality
- changed instructions for phenopype installation: make virtual env in conda for better package control (e.g. avoid different opencv versions)

------
bugfix:
- "filename not found" when no objects were found

------
- full landmark functionality added (refer to "landmark_maker" readme in the docs)
- additionally: measure length of curvy specimens from within the landmarking function ("arc")
- generic image registration (aka feature recognition) added, will be properly introduced and documented in the next version