1. add "-MP" prevents make-level errors when switching IDF versions, as headers may be removed
2. add macro "IS_BOOTLOADER_BUILD" to disable link file generation when compiling bootloader
3. add "<:" to avoid makefile to search it undefined variable
1. support "make size", "make size-files", "make size-components" and "make size-symbols"
2. add esp-idf style link file including "esp8266.ld" and "esp8266.project.ld.in"
3. add link advaced generation file to components of esp8266 and spi_flash
1. APP binary supports 4KB align instead of 64KB align
2. Add options to sdkconfig.defaults:
2.1. using 1MB flash
2.2. use custom partition table "partitions_two_ota.1MB.mini.csv"
2.3. custom partition table base address is 0x4000
3. "make ota flash" using APP1_OFFSET as app downloading address
"$(PROJECT_NAME).app1.bin", "$(PROJECT_NAME).app2.bin" and "$(PROJECT_NAME).ota.bin" at "build" directory.
Only upload "$(PROJECT_NAME).ota.bin" to the server.
Select the target flash and input "make ota flash" or "make ota flash monitor".
Update the OTA README.md for 1 MB flash.
1. support save cal data in nvs;
2. support use phy partition to store init data;
In old SDK, we use (max_sec - 3) as init data sector, and (max_sec - 4) as cal data sector. This is changed in IDF style SDK, and these 2 sectors can be used for other perpose.
1. support generating esp8266 specific bin when input 'make' and so on
2. support 'make flash', 'make monitor' and 'make monitor flash'
3. esp8266 do not support secure boot
