add core_esp8266_features.h to be able to detect the features and librarys included in the ESP core
add core_esp8266_features.h to be able to detect the features and librarys included in the ESP core

jes/Arduino,gguuss/Arduino,jes/Arduino,esp8266/Arduino,hallard/Arduino,Juppit/Arduino,toastedcode/esp8266-Arduino,NullMedia/Arduino,NextDevBoard/Arduino,KaloNK/Arduino,Lan-Hekary/Arduino,NullMedia/Arduino,KaloNK/Arduino,quertenmont/Arduino,edog1973/Arduino,hallard/Arduino,Juppit/Arduino,lrmoreno007/Arduino,toastedcode/esp8266-Arduino,jes/Arduino,quertenmont/Arduino,sticilface/Arduino,gguuss/Arduino,Lan-Hekary/Arduino,quertenmont/Arduino,KaloNK/Arduino,wemos/Arduino,edog1973/Arduino,hallard/Arduino,NullMedia/Arduino,toastedcode/esp8266-Arduino,esp8266/Arduino,Adam5Wu/Arduino,quertenmont/Arduino,lrmoreno007/Arduino,martinayotte/ESP8266-Arduino,Links2004/Arduino,jes/Arduino,lrmoreno007/Arduino,lrmoreno007/Arduino,me-no-dev/Arduino,edog1973/Arduino,hallard/Arduino,Adam5Wu/Arduino,KaloNK/Arduino,esp8266/Arduino,me-no-dev/Arduino,me-no-dev/Arduino,NextDevBoard/Arduino,martinayotte/ESP8266-Arduino,Adam5Wu/Arduino,Adam5Wu/Arduino,sticilface/Arduino,quertenmont/Arduino,esp8266/Arduino,martinayotte/ESP8266-Arduino,wemos/Arduino,edog1973/Arduino,KaloNK/Arduino,Juppit/Arduino,Links2004/Arduino,edog1973/Arduino,Lan-Hekary/Arduino,NullMedia/Arduino,Links2004/Arduino,gguuss/Arduino,sticilface/Arduino,esp8266/Arduino,me-no-dev/Arduino,sticilface/Arduino,NextDevBoard/Arduino,Juppit/Arduino,me-no-dev/Arduino,Lan-Hekary/Arduino,wemos/Arduino,NextDevBoard/Arduino,Juppit/Arduino,NextDevBoard/Arduino,gguuss/Arduino,martinayotte/ESP8266-Arduino,Lan-Hekary/Arduino,martinayotte/ESP8266-Arduino,lrmoreno007/Arduino,Links2004/Arduino,sticilface/Arduino,gguuss/Arduino,Adam5Wu/Arduino,hallard/Arduino,jes/Arduino,wemos/Arduino,Links2004/Arduino,wemos/Arduino,toastedcode/esp8266-Arduino,toastedcode/esp8266-Arduino,NullMedia/Arduino