added 'ret' and implemented a proper 'strcmp'

tests/ret_test.expected

@@ -0,0 +1 @@
+g

tests/ret_test.sl

@@ -0,0 +1,11 @@
+import stdlib.sl
+
+word g
+    "g" puts
+    ret
+    "g" puts
+end
+
+word main
+    g
+end

tests/str.expected

@@ -1,4 +1,3 @@
 1
-g
-g
+0
 hello world hello world hello world hello world hello world

tests/str.sl

@@ -1,11 +1,13 @@
 import stdlib.sl
 
 word main
-    "g" "g"
+    "ggggggggh" "ggggggggh"
+    strcmp
+    puti cr
+
+    "ggggggggh" "ggggggggd"
     strcmp
     puti cr
-    puts
-    puts
 
     "hello world hello world hello " "world hello world hello world"
     strconcat