[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

core/furi/memmgr.c

@@ -68,6 +68,12 @@ size_t memmgr_get_minimum_free_heap(void) {
     return xPortGetMinimumEverFreeHeapSize();
 }
 
+void* furi_alloc(size_t size) {
+    void* p = malloc(size);
+    furi_check(p);
+    return memset(p, 0, size);
+}
+
 void* __wrap__malloc_r(struct _reent* r, size_t size) {
     void* pointer = malloc(size);
     return pointer;