Update path.class.js

Modified path positioning, fixes svg 170, debian logo, change some errors in different errors.
there were 4 multiply by 0.5 , at the end is equal to one by 0.25 if you check the original code.
px is created  adding x and y both multiplyed by 0.5 , same for py. then they both get multiplied by themselves. so 0.5 get 0.25 on both. so at the end you can just multiply the sum of those by 0.25. just to reduce the number of multiply used.