videoread module for retrieving frames from video
Improve config handling and docstrings

ffmpeg path now set in user_config.py; example file is updated to reflect
this.
Created vidtools module

Contains class for opening and controlling iteration through frames of
videos.
Started stage shift correction and got framegen
Merge commit
fixed vidtools bugs
Finished off video reading tools, started contours

Video reading is slow and RAM-intensive but works. Contours are easy to
find.
Created Worm class

Smooths image data and segments using the length down each side.
Interim commit for PC moving
hacking day
further hacking
Improved get_pointiness
New MinimalWormSpecification class using openCV to segment
Merge branch 'home' of https://github.com/clbarnes/movement_validation into opencv
Tidied up files, started extending Video class