[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.h

@@ -1,3 +1,8 @@
+/**
+ * @file icon.h
+ * GUI: Icon API
+ */
+
 #pragma once
 
 #include <stdint.h>
@@ -8,10 +13,28 @@ extern "C" {
 
 typedef struct Icon Icon;
 
+/** Get icon width 
+ *
+ * @param[in]  instance  pointer to Icon data
+ *
+ * @return     width in pixels
+ */
 uint8_t icon_get_width(const Icon* instance);
 
+/** Get icon height
+ *
+ * @param[in]  instance  pointer to Icon data
+ *
+ * @return     height in pixels
+ */
 uint8_t icon_get_height(const Icon* instance);
 
+/** Get Icon XBM bitmap data
+ *
+ * @param[in]  instance  pointer to Icon data
+ *
+ * @return     pointer to XBM bitmap data
+ */
 const uint8_t* icon_get_data(const Icon* instance);
 
 #ifdef __cplusplus