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/module/multiple_variables/module.wren

@@ -0,0 +1,8 @@
+// nontest
+var Module1 = "from module one"
+var Module2 = "from module two"
+var Module3 = "from module three"
+var Module4 = "from module four"
+var Module5 = "from module five"
+
+IO.print("ran module")

test/language/module/multiple_variables/multiple_variables.wren

@@ -0,0 +1,10 @@
+import "module" for Module1, Module2, Module3, Module4, Module5
+
+// Only execute module body once:
+// expect: ran module
+
+IO.print(Module1) // expect: from module one
+IO.print(Module2) // expect: from module two
+IO.print(Module3) // expect: from module three
+IO.print(Module4) // expect: from module four
+IO.print(Module5) // expect: from module five