std::function support for SAMD

[rueckix]

I found that ARDUINO_ARCH_SAMD does not imply HAS_FUNCTIONAL in group_object.h even though SAMD supports this c++11 template. I believe support for SAMD should be added here unless there is a specific reason not to.

Why would one need this?
This is quite useful when using callbacks on group objects. When modelling a device as a class, the callback is typically a non-static member function that cannot be passed as a regular function pointer.
An elegant solution is to combined std::bind with std::function to register a member function of a specific class object.

Implications
The change is simple but including STL headers conflicts with the definition of max and min macros in the arduino framework for SAMD. This should be fixed in arduino/ArduinoCore-samd#399 but not released.
Per interim, a hacky

#undef max
#undef min

is required before including STL headers.

Opinions?

[thelsing]

you could add these undefs to bits.h as (with #ifdef arduiono_samd) . We can remove them if the arduino core gets fixed. Feel free to submit a pull request.

[rueckix]

PR open