Allow asynchronous loading of CoinWidget

Currently, CoinWidget needs to wait until the `coin.js` script is loaded, blocking the loading of a page.

	<script src="coin.js"></script>
	<script>
	//Synchronous: the script needs to be loaded before this function can be called and the widget will be created at the place where the function is called. It isn't possible to call it after page load.
	CoinWidgetCom.go({

		/* make sure you update the wallet_address or you will not get your donations */
		wallet_address: "122MeuyZpYz4GSHNrF98e6dnQCXZfHJeGS"

		, currency: "bitcoin"
		, counter: "count"
		, alignment: "bl"
		, qrcode: true
		, auto_show: false
		, lbl_button: "Donate"
		, lbl_address: "Donate Bitcoin to this Address:"
		, lbl_count: "donations"
		, lbl_amount: "BTC"
	});
	</script>
With the new code, it will be possible to do it as follows:

    <span id='put_coinwidget_here'></span>
    <!--The rest of the HTML document-->
    Bottom of the page:
    <script src='coin.js'></script>
	//Asynchronous: replace an element with the CoinWidget
	CoinWidgetCom.go({

		/* make sure you update the wallet_address or you will not get your donations */
		wallet_address: "122MeuyZpYz4GSHNrF98e6dnQCXZfHJeGS"

		, currency: "bitcoin"
		, counter: "count"
		, alignment: "bl"
		, qrcode: true
		, auto_show: false
		, lbl_button: "Donate"
		, lbl_address: "Donate Bitcoin to this Address:"
		, lbl_count: "donations"
		, lbl_amount: "BTC"
	}, "#put_coinwidget_here");