Implement namespaces

This includes a massive refactoring of the type checker, getting
rid of most of the ets tables and keeping a proper environment.

test/contracts/namespaces.aes

@@ -0,0 +1,31 @@
+
+namespace Lib =
+
+  // namespace Internal =
+  //   function rev(xs, ys) =
+  //     switch(xs)
+  //       []      => ys
+  //       x :: xs => rev(xs, x :: ys)
+  private
+    function rev(xs, ys) =
+      switch(xs)
+        []      => ys
+        x :: xs => rev(xs, x :: ys)
+
+  function reverse(xs : list('a)) : list('a) = rev(xs, [])
+
+  function eqlist(xs : list(int), ys : list(int)) =
+    switch((xs, ys))
+      ([], [])           => true
+      (x :: xs, y :: ys) => x == y && eqlist(xs, ys)
+      _                  => false
+
+contract TestNamespaces =
+
+  record state = { x : int }
+
+  function init() = { x = 0 }
+
+  function palindrome(xs : list(int)) : bool =
+    Lib.eqlist(xs, Lib.reverse(xs))
+