Also simplify project structure. The executable is now produced in
the root directory. Work in progress.

So multiple successive incremental Evals function correctly.

Also improve the following:
- Apply the same Eval API to vm0 and vm1
- parser: dot diagram display is now synchronous
- codegen: outsource complex code generation for readability
- vm1: Pop take the number of values to pop as operand

This makes the code easier to use.

* codegen: add a bytecode generator
* cleaning scanner, parser and vm1.

* vm1: add file pos for debug and a few immediate instructions

`op[0]` is now reserved for storing the file position computed at
code compiling. No impact on performances.

Added `Subi` and `Infi` which use integer immediate argument instead
of stack. Experimental. Improves `fib()`  speed by ~ 20%.

* vm1: add benchmark as proposed by @ajnavarro