Add PHP 8 support

[strangerkir]

This package requires PHP ^5.4 | ^7.0. It would be useful to add PHP 8 support. Also, it blocks upgrading dhii/wp-events package to use PHP 8.

[XedinUnknown]

This repo is obsolete, and not really used at least right now. This was an attempt to make the exception framework of PHP more usable, as it is pretty ambiguous right now, and not very helpful: \InvalidArgumentException does not provide any info about which argument is invalid, etc. For now, I would suggest leaving this repo alone, and refactor dependencie where necessary and possible.