Move the plugin examples to subdir of pluginhowto.

doc/pluginhowto/examples/progressbar/progressbarplugin.h

@@ -0,0 +1,20 @@
+#ifndef PROGRESSBAR_PLUGIN_H
+#define PROGRESSBAR_PLUGIN_H
+
+#include <extensionsystem/iplugin.h>
+
+class ProgressBarPlugin : public ExtensionSystem::IPlugin
+{
+    Q_OBJECT
+
+public:
+    ProgressBarPlugin();
+    ~ProgressBarPlugin();
+
+    void extensionsInitialized();
+    bool initialize(const QStringList & arguments, QString* errorString);
+    void shutdown();
+};
+
+#endif // PROGRESSBAR_PLUGIN_H
+