Doc: edit coreplugin docs

Remove \brief commands for functions.
Use standard wording for QDoc commands.
Fix style and grammar issues.
Use the \a command instead of the \c command for attributes
in function descriptions.
Do not use \returns, because it does not exist.

Change-Id: Icd32b519670cb376e246bab3a58fe7e98d2529ea
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/dialogs/ioptionspage.cpp

@@ -39,15 +39,16 @@
   into the plugin manager object pool (e.g. ExtensionSystem::PluginManager::addObject).
   Guidelines for implementing:
   \list
-  \li id() is a unique identifier for referencing this page
-  \li displayName() is the (translated) name for display
-  \li category() is the unique id for the category that the page should be displayed in
-  \li displayCategory() is the translated name of the category
-  \li createPage() is called to retrieve the widget to show in the preferences dialog
+  \li \c id() is a unique identifier for referencing this page
+  \li \c displayName() is the (translated) name for display
+  \li \c category() is the unique id for the category that the page should be displayed in
+  \li \c displayCategory() is the translated name of the category
+  \li \c createPage() is called to retrieve the widget to show in the
+        \gui Options dialog
      The widget will be destroyed by the widget hierarchy when the dialog closes
-  \li apply() is called to store the settings. It should detect if any changes have been
+  \li \c apply() is called to store the settings. It should detect if any changes have been
          made and store those
-  \li finish() is called directly before the preferences dialog closes
-  \li matches() is used for the options dialog search filter
+  \li \c finish() is called directly before the \gui Options dialog closes
+  \li \c matches() is used for the \gui Options dialog search filter
   \endlist
 */