Make 'void'... well nothing

[TropicSapling]

Could allow something like this:

func f (SomeType arg) (void|SomeType opt_arg) -> SomeType { // To be consistent, I guess it should also be allowed to just simply write '|SomeType'
    ...
}

f 123 void; // How you would write it rn
f 123; // How you could write it if 'void' was the same as nothing
f 123 456; // Using all args