Release for Homie-ESP8266 v3.0.0

Update example.cpp

Added InputPinArrayNode

New InputPinArrayNode for simple IO + doc improvements

+ InputPinArrayNode can be used to define a vector of GPIOs that are
configured as INPUT_PULLUP and announced as array of Contacts.
+ created doxyfile for doc generation with doxygen
+ added some doxygen-style doc-strings
+ small refactoring of RelaisNode

v0.8.0

Fix Homie version