+ Renamed old crop_images fn to dynamic_crop_images

# Conflicts:
#	README.md
#	process/batch_processing.py
#	tests/test_process_batch.py

+ Renamed old crop_images fn to dynamic_crop_images

Development

See merge request cribe001/dlc_flytracker!13

Improve README based on fresh user experience

See merge request cribe001/dlc_flytracker!12

The 'brightness', 'sharpness' and 'color' variants of 'enhance_images'
all called 'enhance_color'.

Running `test_skeleton_fitter.py` as a script will still show the plots,
but for convenience of running the test suite from the command line,
they are not shown anymore when executed with `pytest`.

`pytest` needs to be executed from `tests/`, since the tests all
assume paths relative to this directory.

This makes them easier to copy-paste into the terminal or an editor.

Most MarkDown renderers only recognise paragraphs if they are
separated by an empty line.

The added how-to was based on a clean installation on a new machine.

The version ranges indicated previously were too broad, making it difficult
for pip to resolve dependency conflicts. The relatively narrow version ranges
indicated here were tested to work.