Add some basic programs

programs/data_decls.lily

@@ -0,0 +1,2 @@
+data Bool = { True, False }
+data IntList = { Nil, Cons(Int, IntList) }

programs/length.lily

@@ -0,0 +1,6 @@
+defn length l = {
+    case l of {
+        Nil -> { 0 }
+        Cons(x, xs) -> { 1 + length xs }
+    }
+}

programs/not.lily

@@ -0,0 +1,6 @@
+defn not b = {
+    case b of {
+        False -> { True }
+        True -> { False }
+    }
+}