more migration to common docs (#370)

* more migration to common docs

* refactoring js

* removed duplicate docs

* migrating more docs

* more refactoring

* migrated browsers page

* updated summary

docs/blocks/variables/change.md

@@ -0,0 +1,13 @@
+# @extends
+
+## #examples
+
+### Example: show the value of a variable
+
+Use the assignment operator to set the value of a [variable](/blocks/variables/var). Change the value of a variable from 0 to 1 using the change item block. Then display the new value of the variable on the LED screen. Like this:
+
+```blocks
+let x = 0;
+x += 1;
+basic.showNumber(x);
+```