add API to get chip info
This change adds an API to get chip info, such as chip model, enabled capabilities, size of embedded flash, silicon revision.
Hello_world example is modified to print out the information about the chip. The example is also simplified by moving all code into the main task.
Ref TW12031.
See merge request !549
Base MAC address can be stored in default manufacture-defined or customer
pre-defined place in EFUSE and other place e.g. flash or EEPROM.
If choose to use base MAC address which is stored in other place, please
call esp_base_mac_addr_set_external() before initializing WiFi/BT/Ehternet.
1. Add detailed return error code for wifi APIs
2. Add description about error code in esp_wifi.h
3. Modify esp_wifi_reg_rxcb to esp_wifi_internal_reg_rxcb
4. Modify esp_wifi_set_sta_ip to esp_wifi_internal_set_sta_ip
5. Mark system_init as deprecated API
App can contain a stub program resident in RTC fast memory. Bootloader
will load the stub on initial boot. If the device wakes from deep sleep,
the stub is run immediately (before any other data is loaded, etc.)
To implement a custom wake stub, implement a function in your program:
```
void RTC_IRAM_ATTR esp_wake_deep_sleep(void)
{
esp_default_wake_deep_sleep();
// other wake logic
}
```
... and it will replace the default implementation.
