Move newline handling down into parser.

This lets us make it a grammar feature and not a lexer trick.
Newlines are explicitly ignored in some parts of the grammar. This
lets, for example, things like "|" ignore the newline when used as
an operator, but not when used as a parameter delimiter in a block
argument.

test/if/else.wren

@@ -4,7 +4,3 @@ if (false) IO.print("bad") else IO.print("good") // expect: good
 
 // Allow block body.
 if (false) null else { IO.print("block") } // expect: block
-
-// Newline after "else".
-if (false) IO.print("bad") else
-IO.print("good") // expect: good