Documentation for parts of the VM

[sin-ack]

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.