(interpreter) Warn on ambiguous combination of boolean operators

[perlun]

This has been an idea of mine since a long time. Quoting #245:

Doing things which are considered "hard-to-from" from an ambiguity should produce a compile-time error. I am thinking about expressions like this:

true && false || false

Without digging up a book/Internet resource, can you by heart say what the above will produce in the language you use everyday?

(The right answer is typically false since || has higher precedence than &&. In other words, the above should be read as true && (false || false).)

What Perlang aims to do here

We want to make it impossible to write the above, ambiguous code. The compiler should complain and enforce the usage of clarifying parentheses in this case.

Closes #245.