removed old extension guide, renamed new extension guide

Author: Florian

README.md

@@ -21,9 +21,8 @@ This is the documentation for [Pagekit](https://pagekit.com), a modular open sou
   8. [Finder](user-interface/finder.md)
 
 - Tutorials
-  1. [How to: Extension](developer-guides/todo-extension.md)
+  1. [How to: Extension](developer-guides/extension.md)
   2. [How to: Theme](developer-guides/how-to-theme.md)
-  2. [Extensions](developer-guides/extensions.md)
   3. [Themes](developer-guides/themes.md)
   4. [Widgets](developer-guides/widgets.md)
   5. [Dashboard Widgets](developer-guides/dashboard-widgets.md)

developer-basics/packages.md

@@ -20,7 +20,7 @@ A package contains at least two files.
 1. The `composer.json` contains the metadata for your package and therefore acts as the package definition.
 2. The `index.php` is a so called [Module definition](modules.md) and adds actual functionality to Pagekit.
 
-The rest of the package content depends on the package's `type`. To learn more about the actual content of a package, check out the [Theme Guide](../developer-guides/themes.md) or the [Extension Guide](../developer-guides/extensions.md).
+The rest of the package content depends on the package's `type`. To learn more about the actual content of a package, check out the [Theme Guide](../developer-guides/themes.md) or the [Extension Guide](../developer-guides/extension.md).
 
 ## Package definition
 A package is defined by its `composer.json`. This file includes the package name, potential dependencies to be installed by [Composer](https://getcomposer.org) and other information that displays in the Pagekit marketplace.

developer-guides/todo-extension.md renamed to developer-guides/extension.md

@@ -6,6 +6,6 @@ Depending on your goals with Pagekit you might want to read only pieces of the d
 
 1. Pagekit [installation](installation.md), [requirements](requirements.md) and places to [find help](../getting-started/getting-help.md) if you are stuck.
 2. Learn how to use the Pagekit [user interface](../user-interface/dashboard.md).
-3. To get started as a developer, learn [how to create an extension](../developer-guides/extensions.md) and [how to build a theme](../developer-guides/themes.md).
-4. For a complete video guide on building an extension, watch [the screencast about an example extension](../developer-guides/todo-extension.md).
+3. To get started as a developer, learn [how to create an extension](../developer-guides/extension.md) and [how to build a theme](../developer-guides/themes.md).
+4. For a complete video guide on building an extension, watch [the screencast about an example extension](../developer-guides/extension.md).
 5. For more fundamental developer topics, read up on e.g. [packages](../developer-basics/packages.md), [modules](../developer-basics/packages.md) and [packages](../developer-basics/routing.md).