add HIMEM debugging tools (check free size, and memory test) (#1852)

* Update defines.h

* Update esp_sys.h

* Update esp_sys.cpp

* Add files via upload

* Update perfmon.c

* Update main.cpp

* Update main.cpp

* Delete himem_memory_check.c

* Add files via upload

* Update defines.h

* Update himem_memory_check.cpp

* Update main.cpp

* Update himem_memory_check.cpp

* Update himem_memory_check.h

* Update main.cpp

code/components/jomjol_helper/perfmon.c

@@ -2,6 +2,23 @@
 
 #include "../../include/defines.h"
 
+/*
+ESP32 CPU usage monitor
+Gives you a rough idea of how the Xtensa cores are utilized.
+
+Works by attaching idle hooks and measuring how often they get called. The core usage is calculated: usage% = idle ticks since last measurement / expected idle ticks if core were idle * 100%. The expected idle tick count was measured by running an empty program.
+
+Limitations:
+Should only be used for user information, not in logic that needs accurate values
+New IDF versions could optimize performance and therefore introduce an error to usage estimation.
+When one core is at 100% the other might report a negative value
+
+Usage:
+#include "perfmon.h"
+Call perfmon_start() once
+
+*/
+
 #ifdef DEBUG_ENABLE_PERFMON
 
 #include "perfmon.h"
@@ -67,4 +84,4 @@ esp_err_t perfmon_start()
 }
 
 
-#endif // DEBUG_ENABLE_PERFMON
+#endif // DEBUG_ENABLE_PERFMON