Add web front-end and fix API issues

node_modules/concurrently/dist/lib/date-format.d.ts

@@ -0,0 +1,19 @@
+export interface FormatterOptions {
+    locale?: string;
+    calendar?: string;
+}
+/**
+ * Unicode-compliant date/time formatter.
+ *
+ * @see https://unicode.org/reports/tr35/tr35-dates.html#Date_Format_Patterns
+ */
+export declare class DateFormatter {
+    private readonly options;
+    private static tokenRegex;
+    private readonly parts;
+    constructor(pattern: string, options?: FormatterOptions);
+    private compileLiteral;
+    private compileOther;
+    private compileToken;
+    format(date: Date): string;
+}