Replace GPIO sysfs interface for interrupts with GPIO character device

[golemparts]

The GPIO sysfs interface (/sys/class/gpio) has been deprecated, with the relatively new GPIO character device (/dev/gpiochipN) interface offered as a replacement. Since GPIO sysfs is currently used for interrupts, a migration to the GPIO cdev interface needs to happen before GPIO sysfs is removed (after 2020).

As an added benefit, this is also a workaround for a bug in Fedora where GPIO sysfs doesn't properly handle interrupts.

[golemparts]

All of the existing interrupt methods now use the new GPIO character device interface. On Raspbian they're working as intended.

[KuabeM]

As well as on Fedora - thank you, great job!

[golemparts]

@KuabeM excellent! Thanks for testing on Fedora. 0.8.0 will be released as soon as the PWM and UART modules have been completed and documented, which will likely be later this month. Of course you can always stay on the master branch if you want to move back to Fedora sooner.