Test suite, documentation, code restructuring + improved UI, bug fixes.

Test suite: we wrote an end-to-end test procedure and two unit tests: to check the open and save photos function and to check each image processing function. Documentation: we added many more inline comments in various places to make the code more evident and a documentation markdown file that explains what every function does. Code restructuring: we gave most image processing functions their own files for readability and to make unit testing easier. We also organized the files more clearly into different folders. UI: when the script is run, we add a description explaining what each function does on the terminal. Bug fixes: the scale function didn't always work because the x and y values weren't always converted to strings, so that was fixed. We also added the photos we got from Luke from the original experiment that this tool was meant to help with.