Make initialization and de-initialization less intrusive

[arne48]

Currently during initialization and after de-initialization the library sets all pins as inputs.
This can cause problems when some pins are used by other programs as the IOMUX is changed.
Further does the header not provide the same functionalities after the library ran once.

It would be nicer if during initialization all possibly changing parameters of the pins are saved and restored during de-initialization. Further shouldn't all pins be reset on start but just those which are actually used should be configured.