restructuring to separate language from API

docs/blocks/loops/for.md

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+# For
+
+### @parent blocks/language
+ 
+Run part of the program the number of times you say.
+
+### Example: Count to 4
+
+This program will show the numbers 0, 1, 2, 3, and 4 one after another on the LED screen.
+
+```blocks
+for(let i = 0; i < 5; ++i) {
+basic.showNumber(i)
+}
+```
+
+### See also
+
+[repeat](/blocks/loops/repeat), [while](/blocks/loops/while), [if](/blocks/logic/if), [show number](/reference/basic/show-number)
+