[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/pipeline.h

@@ -41,6 +41,7 @@ void pipeline_refine_lvalue_for_mutate_arguments();
 void pipeline_check_rvalue_lvalue();
 void pipeline_check_pure_impure_operations();
 void pipeline_constant_folding();
+void pipeline_optimize_boolean_expressions();
 void pipeline_convert_ast_to_legacy_Expr_Op();
 
 void pipeline_find_unused_symbols();