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/number/literals.wren

@@ -0,0 +1,10 @@
+IO.print(123)     // expect: 123
+IO.print(987654)  // expect: 987654
+IO.print(0)       // expect: 0
+IO.print(-0)      // expect: -0
+
+IO.print(123.456) // expect: 123.456
+IO.print(-0.001)  // expect: -0.001
+
+// TODO: Scientific notation?
+// TODO: Literals at and beyond numeric limits.