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.

applications/ibutton/ibutton-cli.cpp

@@ -255,7 +255,6 @@ void onewire_cli_search(Cli* cli) {
             printf("Search finished\r\n");
             onewire.reset_search();
             done = true;
-            return;
         } else {
             printf("Found: ");
             for(uint8_t i = 0; i < 8; i++) {