link: introduce effects #850 #1008

- new link effects: target download
- effects can now be strings besides bools (to allow for custom download
  attribute on links)
- remove "no*" classes form image as they don't make sense for
  string effects and are cluttering the image class list for newly
  introduced effects
- refactor attribute parsing for later reusage in menu generation, button
  topbar, etc.

docs/content/introduction/quickstart/_index.en.md

@@ -127,7 +127,7 @@ Open [http://localhost:1313](http://localhost:1313) in your web browser.
 
 You can keep the server running while you edit. The browser will update automatically when you save changes.
 
-{{% figure src="magic.gif" link="https://gohugo.io" alt="Magic" caption="It's a kind of magic" %}}
+{{% figure src="images/magic.gif" link="https://gohugo.io" alt="Magic" caption="It's a kind of magic" %}}
 
 ## Build and Deploy