squeeze out some performance

[Robert Voigtländer]

> Actually for optimised code it looks very similar to some code posted 
> 
> here 
> 
> http://www.daniweb.com/software-development/python/threads/321181/python-bresenham-circle-arc-algorithm 
> 
> over three years ago.
> 

This is where it origins from. I just extended it for my needs and now want to optimize it.
List comprehensions instead of some for loops brought another 25%. And made the code shorter.