replace range -> xrange in polytope
replace len(poly) > 0 check by isinstance(poly, Region)
rename variable: list -> lst

to avoid shadowing the built-in function of the same name
simplify variable names for subsystems in continuous_pwa

because they now each subsystem is created in its own function
style continuous_pwa, improve comment
use Polytope.scale in continuous_pwa

to improve readability