The WLAN.config() method now supports "ssid", "security" and "key" as
aliases to the existing "essid", "authmode" and "password", which are now
deprecated. The help text and setup helper are also updated.
Addresses issue #8083.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.