More efficient stack management

More efficient stack management

Vectors are better than lists, since they don't need to allocate new
memory for every element.  A suitably sized reserve() does away with any
initial reallocations in most cases.

ProgramData in Renderer can be stored in a semi-independent stack as
well, since it can only be removed with a pop.  State is now devoid of
dynamically allocated memory, making the stack operations even faster.