Removes reference to register_uninstall_hook from code comment

Perhaps mention uninstall.php in stead?

```
// Register hooks that are fired when the plugin is activated or deactivated.
// When the plugin is deleted, the uninstall.php file is loaded.
```
Mention uninstall.php in code comment
Removes 'Change 'plugin-name' to the name of your plugin' from DocBlock

Removes 'Change 'plugin-name' to the name of your plugin' from add_plugin_admin_menu() function DocBlock, as this is now defined via a variable.
Replace plugin-name with $this->plugin_slug in add_action_links()
Merge pull request #79 from barryceelen/patch-2

Removes 'Change 'plugin-name' to the name of your plugin' from DocBlock
Merge pull request #80 from barryceelen/patch-3

Replace plugin-name with $this->plugin_slug in add_action_links()
Merge pull request #77 from barryceelen/patch-1

Removes reference to register_uninstall_hook from code comment