Renames keyboard folder to keyboards, adds couple of tmk's fixes (#432)

* fixes from tmk's repo

* rename keyboard to keyboards

tmk_core/common/host.c

@@ -86,7 +86,7 @@ void host_consumer_send(uint16_t report)
     (*driver->send_consumer)(report);
 }
 
-uint16_t host_last_sysytem_report(void)
+uint16_t host_last_system_report(void)
 {
     return last_system_report;
 }