Redesign sleep() functions

- unified sleeping function _sleep(), including smartSleep
- prevent sleeping if transport is not ready
- add debug log messages

core/MyHwESP8266.cpp

@@ -93,7 +93,7 @@ void hwWriteConfig(int adr, uint8_t value)
 int8_t hwSleep(unsigned long ms) {
 	// TODO: Not supported!
 	(void)ms;
-	return -2;
+	return MY_SLEEP_NOT_POSSIBLE;
 }
 
 int8_t hwSleep(uint8_t interrupt, uint8_t mode, unsigned long ms) {
@@ -101,7 +101,7 @@ int8_t hwSleep(uint8_t interrupt, uint8_t mode, unsigned long ms) {
 	(void)interrupt;
 	(void)mode;
 	(void)ms;
-	return -2;
+	return MY_SLEEP_NOT_POSSIBLE;
 }
 
 int8_t hwSleep(uint8_t interrupt1, uint8_t mode1, uint8_t interrupt2, uint8_t mode2, unsigned long ms) {
@@ -111,7 +111,7 @@ int8_t hwSleep(uint8_t interrupt1, uint8_t mode1, uint8_t interrupt2, uint8_t mo
 	(void)interrupt2;
 	(void)mode2;
 	(void)ms;
-	return -2;
+	return MY_SLEEP_NOT_POSSIBLE;
 }
 
 ADC_MODE(ADC_VCC);