Example: foreach ($coords as list($x, $y)) { ... }
This change slightly breaks backwards compatability, as it changes the
node structure for the previously existing `list(...) = $foo` assignments.
Those no longer have a dedicated `AssignList` node; instead they are
parsed as a normal `Assign` node with a `List` as `var`. Similarly the
use in `foreach` will generate a `List` for `valueVar`.
The new dereferencing syntaxes (new Foo)->bar and (new Foo)['bar'] were
causing a shift/reduce conflict with the '(' expr ')' rule. When
(new Foo) was encountered (without dereference operators following) the
parser thus threw a parse error.
The fix simply adds a special '(' new_expr ')' rule to expr. This does not
remove the shift/reduce conflict itself, but makes it irrelevant.
This fixes issue #20.
