Rewrite bootstrap script for clarity

Hello,

I rewrote the install script for some mysterious reason. As short and uninteresting as it was, I suppose something irked me about it and I rewrote it. The changes are all cosmetic, except for the `stream.isatty()` check, which hardly matters. 

Feel free to ignore this :)

Regards,
Georgi
Relax please. Unqualified imports are fine. This is also a 50 line script.