Move and rename showDebugger() method

[nateplusplus]

1. showDebugger is basically a helper function that doesn't need to be part of the pushIn class.
2. It's not really a debugger either, it shows the current scrollY value. Should be named something more appropriate.

This could be moved into a new class and could be called like:

import { PushInScrollHelper } from pushin;

PushInScrollHelper::show();

I think it should still be included on the global scope too, for those who are using a CDN.

pushInScrollHelper();