Better memory management

[dd86k]

At the moment, the mu_Context stacks are all static memory buffers, so a multibyte POD structure really isn't fitted to be put on the stack (just had an issue with the demo having a 4MB struct on stack, poor MSVC).

While dynamically allocating memory in games is often frowned upon, I'm currently thinking what strategies I should employ (e.g., allocating enough at init).

• [x] TODO: Fix current issue with context on stack and move it to heap (I'm at work)