various docs updates

docs/reference/loops.md

@@ -0,0 +1,26 @@
+# Loops
+
+Repeat code.
+
+
+[for](/reference/loops/for)
+
+```blocks
+for(let i = 0;i<5;i++) {}
+```
+
+[repeat](/reference/loops/repeat)
+
+![](/static/mb/blocks/contents-0.png)
+
+[while](/reference/loops/while)
+
+```blocks
+while(true) {}
+```
+
+[forever](/reference/basic/forever)
+
+```blocks
+basic.forever(() => {})
+```