To make the migration progress to the new RTOS SDK easier, the new toolchain was renamed to xtensa-esp8266-elf. This makes it possible to have the new and the old toolchain installed in parallel.
The documentation had to be changed due to the relation of module `esp_now` to `esp_wifi` module. In addition, a number of corrections have been made. In the case of documentation, it is impossible to do this in various commits.
