Addition of other markdown files for other categories of must-watch Python videos.

[s16h]

As mentioned in #3, main markdown should be split into more files to categorise videos into:

• "theory/philosophy of python" (meaning core/builtin only)
• "pythonic web dev" (includes requests, beautiful soup, and all those framework talks)
• "pythonic tools/programs" (for things like pyqt, docopt: things to make tools/desktopish programs easier)

Of course, more categories can be added later.