rename "microbit" package to "core" #414 (#270)

* rename "microbit" package to "core" #414

* shouldn't edit the package id.

* updating package.json

* updated the wrong version

* missed updating pxt.json of tests

libs/core/helpers.ts

@@ -0,0 +1,17 @@
+namespace console {
+    export function log(msg: string) {
+        serial.writeString(msg);
+        serial.writeString("\r\n");
+    }
+}
+
+namespace Math {
+    /**
+     * Generates a `true` or `false` value randomly, just like flipping a coin.
+     */
+    //% blockId=logic_random block="pick random true or false"
+    //% help=math/random-boolean color=230
+    export function randomBoolean(): boolean {
+        return Math.random(2) == 0;
+    }
+}