feat: allow overriding of providers via the calendar modules forRoot …

…method

Closes #205

src/calendar.module.ts

@@ -1,4 +1,4 @@
-import { NgModule, ModuleWithProviders } from '@angular/core';
+import { NgModule, ModuleWithProviders, Provider } from '@angular/core';
 import { CommonModule } from '@angular/common';
 import { ResizableModule } from 'angular-resizable-element';
 import { DragAndDropModule, DraggableHelper } from 'angular-draggable-droppable';
@@ -26,6 +26,12 @@ import { CalendarEventTitleFormatter } from './providers/calendarEventTitleForma
 import { CalendarDateFormatter } from './providers/calendarDateFormatter.provider';
 import { CalendarUtils } from './providers/calendarUtils.provider';
 
+export interface CalendarModuleConfig {
+  eventTitleFormatter?: Provider;
+  dateFormatter?: Provider;
+  utils?: Provider;
+}
+
 /**
  * The main module of this library. Example usage:
  *
@@ -99,15 +105,15 @@ import { CalendarUtils } from './providers/calendarUtils.provider';
 })
 export class CalendarModule {
 
-  static forRoot(): ModuleWithProviders {
+  static forRoot(config: CalendarModuleConfig = {}): ModuleWithProviders {
 
     return {
       ngModule: CalendarModule,
       providers: [
-        CalendarEventTitleFormatter,
-        CalendarDateFormatter,
         DraggableHelper,
-        CalendarUtils
+        config.eventTitleFormatter || CalendarEventTitleFormatter,
+        config.dateFormatter || CalendarDateFormatter,
+        config.utils || CalendarUtils
       ]
     };