mbed.h has 'using namespace mbed;', hence some of the files skip
adding required namespace to the code, it is always good to specify the
namespace around the elements in header and `using namespace` in
specific CPP files, instead of all
Compile [ 1.3%]: ESP8266Interface.cpp
[Error] ESP8266Interface.cpp@582,33: cannot declare static function inside another function
[Error] ESP8266Interface.cpp@583,13: cannot convert 'ESP8266Interface (*)()' to 'WiFiInterface*' in return
Failed to build library