libgpio: Add and document gpio interrupt utility functions

[devivanov_proton.me]

Summary

Add utility functions for configuring gpio interrupts and document file operations.

[vexeduxr]

The code looks okay, just a few notes on the man page & comments. I think that the man page should document both GPIO_EVENT_REPORT_DETAIL and GPIO_EVENT_REPORT_SUMMARY.
Also adding @ziaee for review.

lib/libgpio/gpio.3

167

I think referring to the enum in sys/gpio.h here would make more sense.

171

Ditto

174–177

This should clarify that the call will fail only if the pin is configured for interrupts.
Also, gpio_configure_events can't return EINVAL.

198

These should be wrapped at 72 characters.

lib/libgpio/libgpio.h

108–110

[devivanov_proton.me]

Document GPIO_EVENT_REPORT_DETAIL and GPIO_EVENT_REPORT_SUMMARY.
Limit lines to 72 characters.
Clarify gpio_configure_events failures.
Change wording from delivery type to report type.

[vexeduxr]

Looks good, although I think the header should use .In

lib/libgpio/gpio.3

187

I see that the man page uses this further up too. IMO both should be changed to use .In

[devivanov_proton.me]

Change syntax for header documentation, and document return code for gpio_configure_events

[ziaee]

Lots of whitespace at the end of lines, check mandoc -T lint gpio.3.

lib/libgpio/gpio.3

193

One sentence per line, but not sure we should remove EINVAL.

202

217

[devivanov_proton.me]

Fix formatting

[devivanov_proton.me]

One sentence per line, and markup O_NONBLOCK

[devivanov_proton.me]

Fix list width.

[ziaee]

@