[FL-1906] Documentation: add Doxyfile, prepare sources for doxygen. (#741)

* Documentation: add Doxyfile, prepare sources for doxygen.

* Update ReadMe and remove obsolete CLA

* Add contribution guide

* Contributing: update text

* Correct spelling

applications/gui/icon_animation_i.h

@@ -1,3 +1,8 @@
+/**
+ * @file icon_animation_i.h
+ * GUI: internal IconAnimation API
+ */
+
 #pragma once
 
 #include "icon_animation.h"
@@ -13,11 +18,22 @@ struct IconAnimation {
     void* callback_context;
 };
 
-/** Get pointer to current frame data */
+/** Get pointer to current frame data
+ *
+ * @param      instance  IconAnimation instance
+ *
+ * @return     pointer to current frame XBM bitmap data
+ */
 const uint8_t* icon_animation_get_data(IconAnimation* instance);
 
-/** Advance to next frame */
+/** Advance to next frame
+ *
+ * @param      instance  IconAnimation instance
+ */
 void icon_animation_next_frame(IconAnimation* instance);
 
-/** IconAnimation timer callback */
+/** IconAnimation timer callback
+ *
+ * @param      context  pointer to IconAnimation
+ */
 void icon_animation_timer_callback(void* context);