[Tolk] bool type (-1/0 int under the hood)

Comparison operators `== / >= /...` return `bool`.
Logical operators `&& ||` return bool.
Constants `true` and `false` have the `bool` type.
Lots of stdlib functions return `bool`, not `int`.

Operator `!x` supports both `int` and `bool`.
Condition of `if` accepts both `int` and `bool`.
Arithmetic operators are restricted to integers.
Logical `&&` and `||` accept both `bool` and `int`.

No arithmetic operations with bools allowed (only bitwise and logical).

tolk-tester/tests/w7.tolk

@@ -4,7 +4,7 @@ fun test(y: int): int {
   if (y > 0) {
     return 1;
   }
-  return x > 0;
+  return x > 0 ? -1 : 0;
 }
 
 @method_id(2)