Allow final semicolons everywhere

[lukaszcz]

We've discussed that it's more convenient to always allow final semicolons and format to insert them for consistency (except perhaps when the separated thing fits on a single line).

So we would have:

mk@{
  a := 1;
  b := 2;
}

and

[
 1;
 2;
 3;
]

but

[1; 2; 3]

and

case x of
| mk@{a := 1; b := 2} := ..

if the semicolon-separated list is formatted on a single line.