* IMachine: Add an abstract method `is_true` to evaluate an
		expression.
	* StackBasedMachine:
		* `is_true` implementation;
		* `__init__` takes a program in input;
		* `push_onto_stack`: enforce that any element in
		  memory is a `z3.BitVec` element.

	* PushDataOperator: implemented

	* Instruction: init with a pc, no longer with an opcode.
	* StackBasedInstruction: class renamed `ArithmeticOperator`
	* StackBasedMachine: function `put_onto_stack` renamed to
		`push_onto_stack`

	* InstructionBlock functions renaming to express they are
		dealing with tokens rather than Instructions.
	* InstructionBlock: new function to set the pc.
	* Pass 1 implemented: Set the pc of the instruction blocks.

	* Define the internal methods as static.

	- Parser implemented. It returns a control flow graph.

	- The interfaces module was removed. The interfaces are
	distributed across the remaining modules.

	* Instruction
	* Language
	* Machine
		* StackBasedMachine