feat: Shortcut for configuring LazyMapsAPILoader

[sebholstein]

To set a Google Maps API key, you have to write the following code today:

import {provide} from 'angular2/core';
import {ANGULAR2_GOOGLE_MAPS_PROVIDERS, LazyMapsAPILoaderConfig} from 'angular2-google-maps/core';

bootstrap(AppComponent, [
  ANGULAR2_GOOGLE_MAPS_PROVIDERS,
  provide(LazyMapsAPILoaderConfig, {useFactory: () => {
    let config = new LazyMapsAPILoaderConfig();
    config.apiKey = 'mykey';
    return config;
  }})
])

As this is very verbose, we should add this shortcut, as adding an API key is a very common case:

import {provide} from 'angular2/core';
import {ANGULAR2_GOOGLE_MAPS_PROVIDERS, googleMapsAPIKey} from 'angular2-google-maps/core';

bootstrap(AppComponent, [
  ANGULAR2_GOOGLE_MAPS_PROVIDERS,
  googleMapsAPIKey('myKey')
])

[jhuntoo]

How about

import {provide} from 'angular2/core';
import {provideGoogleMaps} from 'angular2-google-maps/core';

bootstrap(AppComponent, [
  provideGoogleMaps({ apiKey: 'myKey' })
])

Which returns an array including ANGULAR2_GOOGLE_MAPS_PROVIDERS and the config object.

It's even more concise, and the "options-style" object could be extended when/if more configuration is needed down the line.

[sebholstein]

You gave me food for thought :)

I researched how other angular 2 related libraries handle the providers stuff. I discovered the angularfire2 and really makes sense to me:

https://github.com/angular/angularfire2/blob/master/docs/5-user-authentication.md#configure-application-in-bootstrap

So I propose this way:

import {provide} from 'angular2/core';
import {lazyMapsAPILoaderConfig} from 'angular2-google-maps/core';

bootstrap(AppComponent, [
  GOOGLE_MAPS_PROVIDERS,
  lazyMapsAPILoaderConfig({ apiKey: 'myKey' })
])

[jhuntoo]

Yeah I like that too - it's clean & clear API!