Multiple covered rectangles

[GoogleCodeExporter]

Currently, each object in theme is allowed to have one covered rectangle. But 
this can change with adding a number, telling how many covered rectangles 
object has (similarly to how is it done with uncovered ones already).

But to avoid braking current themes, it should be checked during generation how 
many numbers describe object. If the amount of numbers is odd (like it is now), 
it is assumed that there is one covered rectangle and line would parsed 
normally. But when amount is even, one number describes how many covered 
rectangles there are and line would be parsed accordingly.

This would allow to make corner objects, bridges or columns connecting floor 
with ceiling etc.

Original issue reported on code.google.com by KoBeW...@gmail.com on 18 Feb 2015 at 7:40