version 0.3.0

New methods:
- peek_frames method for Frames for peeking the first frame
- show method for Frames, VideoFileStream and CoordinateArrays
- 'save_nonzero' method for Frames to directly save nonzero pixel coordinates as CoordinateArrays
- 'get_coordmedian' method for CoordinateArrays
- 'edge_detection' method for Frames

Other changes:
- bug correction: switch frameheight/framewidth when initializing Frames object
- find_nonzero methods now can work with color frames
- apply_backgroundsegmenter method on Frames for background segmentation
- improved logging of processing steps
- many improvements docstrings and code consistency
- added more tests

Commits by Carien Mol and Gabriel Beckers.