add stdio module

examples/stdio.csn

@@ -0,0 +1,17 @@
+(
+    ; we don't have strings yet 👌
+    (ld @stdout 'H') (ld @stdout 'e') (ld @stdout 'l') (ld @stdout 'l') (ld @stdout 'o')
+    (ld @stdout 32) (ld @stdout 'c') (ld @stdout 'r') (ld @stdout 's') (ld @stdout 'n')
+    (ld @stdout '…') (ld @stdout 32)
+
+    (:loop)
+    (ld r0 @stdin)
+    (cmp r0 'a' (<? (j :badchar)))
+    (cmp r0 'z' (>? (j :badchar)))
+    (sub r0 32) ; to uppercase
+    (ld @stdout r0)
+    (j :loop)
+    (:badchar)
+    (ld @stdout '🐈')
+    (j :loop)
+)