Hackathone session: bugfixes and documentation update (#869)

* ReadMe: update flashing scripts section
* Furi: add record exists method to record store.
* FuriHal: early OS init and i2c timeouts based on os ticks.
* Storage: replace malloc with furi_alloc, fix errors found by pvs.
* iButton: properly handle shutdown in cli search command
* SubGhz: proper argument type in sscanf and incorrect position of logging in switch.

core/furi/record.h

@@ -15,6 +15,14 @@ extern "C" {
  */
 void furi_record_init();
 
+/** Check if record exists
+ *
+ * @param      name  record name
+ * @note       Thread safe. Create and destroy must be executed from the same
+ *             thread.
+ */
+bool furi_record_exists(const char* name);
+
 /** Create record
  *
  * @param      name  record name