fix(docs): 1. toggleDarkness() was added to the documentation

1. `toggleDarkness()` was added to the documentation
2. `setTheme()` was renamed to `setActiveTheme()` and Demo was updated

Author: mirismaili

Demo

@@ -25,7 +25,7 @@
 
 Making able the app to switch between material themes at run-time
 
-[![Video](https://raw.githubusercontent.com/mirismaili/AngularMaterialDynamicThemes/master/res/preview0.gif "Video")](https://github.com/mirismaili/AngularMaterialDynamicThemes)
+[![Video](https://raw.githubusercontent.com/mirismaili/AngularMaterialDynamicThemes/a979c0284577993c3f3b1c6acccbb7d6e6994003/res/preview0.gif "Video")](https://github.com/mirismaili/AngularMaterialDynamicThemes)
 
 ***
 
@@ -104,10 +104,10 @@ export class AppComponent {
 
     constructor(private overlayContainer: OverlayContainer) {
         // Set default theme here:
-        this.setTheme('deeppurple-amber', /* darkness: */ false)
+        this.setActiveTheme('deeppurple-amber', /* darkness: */ false)
     }
 
-    setTheme(theme: string, darkness: boolean = null) {
+    setActiveTheme(theme: string, darkness: boolean = null) {
         if (darkness === null)
             darkness = this.isThemeDark
         else if (this.isThemeDark === darkness) {
@@ -127,10 +127,14 @@ export class AppComponent {
 
         this.activeThemeCssClass = cssClass
     }
+    
+    toggleDarkness() {
+        this.setActiveTheme(this.activeTheme, !this.isThemeDark)
+    }
 }
 ```
 
-And change the theme using `setTheme()` whenever you want. ✓
+And change the theme using `setActiveTheme()` (or `toggleDarkness()`) whenever you want. ✓
 
 > **A more detailed instruction can be found here:**
 >

README.md

@@ -1,6 +1,6 @@
 {
   "name": "angular-material-dynamic-themes",
-  "version": "1.0.3",
+  "version": "1.0.4",
   "description": "Making able the app to switch between material themes at run-time",
   "scripts": {
     "README.md-TOC": "node markdown-toc.js -f README.md",