Parametric Computer Case Script v1.1

Okay, fixed the majority of the problems with the script (main problem: something possessed me to use all 'center = true' flags which made everything much more difficult)

Anyway, fixed and updated now.

Supports PSU spot generation (at bottom, fliping of PSU screw spots availible), PCI card slot generation (no brace yet) backpanel generation, and extra spacing.

Future plans:
-Dedicated parametric fan hole cutters
-HDD holder, CD drive slot
-Front panel slots/lights (should be simple.