fix rf init data sector be broken issue, add function
'user_rf_cal_sector_set' which has to be realized in user application
side, for more info, refer to readme
1. Add libssc.a, simple serial console lib.
2. Add libspiffs.a, SPI file system.
3. Add libwps.a to support WPS.
4. Add libespconn.a, Espressif connection lib.
5. Add libespnow.a to support Espressif ESP-NOW.
6. Add libmesh.a, Espressif mesh.
7. Add libnopoll.a, websocket.
8. Add make_lib.sh in "third_party" folder.
9. Add modem-sleep & light-sleep supported.
10. Update libcirom.a to support float IO.
11. Update gen_misc.sh & gen_misc.bat.
12. Update header files, add comments in doxygen style.
13. Update libsmartconfig.a to version 2.5.2.
14. Update libssl.a.
15. Updates driver (PWM/UART/GPIO/SPI/Hardware timer).
16. Update open source codes of third_party.
17. Modify "ld" files, "dram0 len" should be 0x18000 in RTOS SDK.
18. Remove header files in extra_include, which are already in compile folder.
19. Other APIs sync from non-OS SDK, more details in documentation "20B-ESP8266__RTOS_SDK_API Reference".
20. Other optimization to make the SDK more stable.
