for kernels 4.8 onwards.

Some very old stuff might break.

Additional fixes for the ISR code and some tweaks here and
there. I've removed the checks for some operations that might
fail when using the gpiomem interface - which is now the default
way of doing things - if your program segfaults, then you
may need to use sudo on it.

Also Makefile tweaks to help improve things somewhat - decided to
read the Makefile manual after some 15 years to updated my make
grey cells somewhat.

New command in the gpio command - readall