Refactor SMA implementation to lib/sma.myc

Move the SMA implementation from examples/err.myc and examples/sma.myc
to a new dedicated file in lib/. This change also cleans up unused code
and improves the SMA logic.

examples/sma.myc

@@ -1,24 +1,12 @@
+;; Output: 5.5
+
 (do
-  (def SMA 
-    (fn [length] 
-      (do
-        (def history (series :float))
-        (push history 0)
-
-		(fn [val] 
-           (do 
-              (def sum (+ val (history 0)))
-			  (push history sum)
-              (/ sum length)
-           ))
-      )))
-
   (def sma20 (SMA 20))
 
-  (def n 100)
-  (while (> n 0) 
-    (do 
+  (def n 1000)
+  (while (> n 0)
+    (do
       (print "val=" n " sma20=" (sma20 n))
       (assign n (- n 1))
     ))
-)
+)