Reorganize tests and benchmark scripts.

Mainly to get rid of one top level directory. But this will
also be useful when there are tests of the embedding API.

test/language/comments/unicode.wren

@@ -0,0 +1,11 @@
+// Unicode characters are allowed in comments.
+//
+// Latin 1 Supplement: £§¶ÜÞ
+// Latin Extended-A: ĐĦŋœ
+// Latin Extended-B: ƂƢƩǁ
+// Other stuff: ឃᢆ᯽₪ℜ↩⊗┺░
+// Emoji: ☃☺♣
+
+// TODO: What about combining characters?
+
+IO.print("ok") // expect: ok