Add FastDigialPin as type

[hreintke]

I do not (yet) have a github fork from your repository so this as an issue.

I am not experienced in c++ templates but looking thru your code and a lot of reading :
When you add :

	template<board::DigitalPin DPIN_>
	using FastDigitalPin = typename FastPinType<DPIN_>::TYPE;
	/// @endcond

}
#endif /* FASTIO_HH */
/// @endcond 

to the end of gpio.h
You add the functionality to use

     FastDigitalPin<DigitalPin::LED> led{PinMode::FASTOUTPUT};

as alternative for

     FastPinType<DigitalPin::LED>::TYPE led2(PinMode::FASTOUTPUT);

Leading to more readable an understandable code

[jfpoilpret]

Hi @hreintke this looks interesting indeed, thank you for this suggestion.
I'll need to check out that this can work in all situations before adding it.
For that, I think the best is to use it in all FastArduino examples and check everything builds OK.

[jfpoilpret]

I'll work on it for next version 1.5.
I'll also need to:

• add API doc
• update tutorial to include this new API

[jfpoilpret]

Issue implemented on master branch as per commit f3485e0
Thanks again for your suggestion!