feat: Add currency support

Add support for formatting currency.
This extends the library to become more useful

numberFormat.js

@@ -36,21 +36,60 @@
 // No, I will not add a LibreJS compatible comment
 // GNU won't support my choice of browser so I won't support their tool
 
+// constant arrays to keep data validated
+const currencyDisplays = ['symbol','narrowSymbol','code','name']
+
 function formatNumbers() {
 
 	const numbers = document.getElementsByTagName("num");
 	const documentLanguage = document.documentElement.lang;
-	const formatter = Intl.NumberFormat(documentLanguage);
+	var formatter = Intl.NumberFormat(documentLanguage);
 
 	for (let num  of numbers) {
 		var number = parseFloat(num.innerHTML);
+
 		if (isNaN(number)) {
-			console.error("[numberFormat.js] ERROR: cannot parse num element: " + num.innerHTML);
+			console.error("[numberFormat.js] ERROR: cannot parse num element: ");
+			console.error(num);
 			continue;
 		}
+
+		if (num.attributes.currency) {
+			var f = _createCurrencyFormatter(num,documentLanguage);
+			if (f !== undefined) {
+				formatter = f;
+			}
+		}
+
 		var formatted = formatter.format(number);
 		num.innerHTML = formatted;
 	}
 }
 
+function _createCurrencyFormatter(num,documentLanguage) {
+	var currency;
+	var currencyDisplay;
+	var currencyData = num.attributes.currency.value.split('-');
+	currency = currencyData[0];
+	if (currencyDisplays.includes(currencyData[1])) {
+		currencyDisplay = currencyData[1];
+	}
+	else {
+		currencyDisplay = "symbol"
+	}
+	try {
+		formatter = Intl.NumberFormat(documentLanguage,{
+			style: 'currency',
+			currency: currency,
+			currencyDisplay: currencyDisplay,})
+		return formatter;
+	} catch (error) {
+		console.error("[numberFormat.js] ERROR: Failed to create NumberFormat");
+		console.error(` - Check that ${currency} is a currency code`);
+		console.error(num)
+	}
+	return undefined;
+}
+
+// ENTRY POINT
 formatNumbers();