Get all interupt pins

[SanciuSargas]

A new function was added to easily get contents of the interrupt register. Because with the current functions some interrupts might be missed if more than one pin triggers before the user calls getLastInterruptPin().

This change will not break existing code as it only includes an extra function and an example of how to use it.

Also the description and the name of getLastInterruptPin() is slightly misleading as it gets only the first pin from all that have triggered an interrupt and not necessarily the last one. Did not change this as that would break current code but might be something to consider.