Add a simple example without Langium

[Lotes]

I wrote a simple handwritten expression parser.

It has:

• print outs like print 123;
• variable declaration like var index = 123;
• variable usage like print index+1;
• binary expressions, like +, -, *, / and %
• unary expressions, like + and -

It worked good so far, even the desired validations I get for free :-) .
Currently there is not much, that can go wrong. Only operators that are not overloaded like string * string cause troubles.

Maybe one of you has more ideas, what to add on top for testing or for language features.

For sure I can add parentheses expressions or assignments in order to make the language "round & sound".

In the end I just wanted to have something framework-agnostic and I think this was proven.