[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-6.tolk

@@ -4,5 +4,5 @@ fun failWhenTernaryConditionNotInt(cs: slice) {
 
 /**
 @compilation_should_fail
-@stderr condition of ternary operator must be an integer
+@stderr can not use `slice` as a boolean condition
  */