Documentation for parts of the VM

I'd like to write some documentation for several parts of the virtual machine in order to make it easy for other people to understand more tricky parts of the virtual machine.

• [ ] Heap (in particular, the garbage collection mechanism)
• [ ] The actor model & execution
• [ ] Object layout on the heap
• [ ] Primitives
• [ ] Bytecode

Note that documentation for Self code will live inside the programming environment.