intro to pir, subs, objects

* creating a sub
* opcodes
* say opcode
* set opcode (int and num)
* set opcode (string and pmc, binding)
* creating pmcs (new, box, unbox)
* aggregate pmcs
* local symbols
* labels and branch opcodes
* iterators
* subroutines
* parameters and arguments
* named, optional, slurpy params
* return values
* tailcalls
* subroutine modifiers
* namespaces
* classes
* methods + method calls
* attributes
* vtable functions
* other PMC types
* compiling to .pbc
* load_bytecode

maybe:
* lexicals
* multisubs