Fix a bunch of test TODOs.

- Added a bunch of tests.
- Removed some TODOs for stuff that's already done.
- Made list literals handle newlines better.

test/list/count.wren

@@ -1,7 +1,3 @@
 io.write([].count)           // expect: 0
 io.write([1].count)          // expect: 1
 io.write([1, 2, 3, 4].count) // expect: 4
-
-// TODO: Literal syntax, including newline handling.
-// TODO: Unterminated list literal.
-// TODO: Subscript operator.

test/list/eof_after_comma.wren

@@ -0,0 +1,2 @@
+[1, 2,
+// expect error

test/list/eof_after_element.wren

@@ -0,0 +1,2 @@
+[1, 2
+// expect error

test/list/newlines.wren

@@ -0,0 +1,14 @@
+// Allow newlines in most places.
+var list = [
+
+"a"
+, "b",
+
+"c", "d"
+
+]
+
+io.write(list[0]) // expect: a
+io.write(list[1]) // expect: b
+io.write(list[2]) // expect: c
+io.write(list[3]) // expect: d