Python workshop

This the complete python workshop, with 5 different exercises:

- echo (basically hello world with stdin/out/err)
- walk (os.walk example, to explore the in-memory file system)
- readwrite (reading/writing files in the in-memory file system)
- mylib (example of how to package and use 3rd party pure Python libraries in addition to the stdlibs)
- pngwrite (use of input/output file channels and 3rd party pure Python libraries to do image processing)