[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/invalid-typing-2.tolk

@@ -1,9 +1,9 @@
 fun main() {
-    var tri: (int, bool) = (10, false);
+    var tri: (int, int) = (10, false);
     return;
 }
 
 /**
 @compilation_should_fail
-@stderr bool type is not supported yet
+@stderr can not assign `(int, bool)` to variable of type `(int, int)`
  */