Added markers
Modifying how the program runs.
Adding a few methods for the program's position.
Modified position methods

Added goto_marker method.
Updated opcodes
Opcodes now handle the program's position.
Removed Opcode's get_id and get_name methods
Added halt opcode
Removed unneeded includes
Made memory member variable public

This will most likely be later changed to handle scopes and whatnot.
Fixed Program forward declaration.
Fixed bugs