eplug is a plugin manager for portage that allows you to make portage do what you want it to a little bit easier!
You can install eplug from basil-overlay
Then uncomment/add lines in /etc/portage/plugins.load to enable plugins from /etc/portage/plugins/
If you want to continue to use the original ehook instead of migrating to the eplug version then you are safe to continue using the v1.1 tag
If you want to migrate from the original ehook to the eplug port of legacy ehook then you can just install eplug normally, rename package.ehook to hook, and uncomment the legacy/ehook line in /etc/portage/plugins.load
If you'd like to migrate to the modern ehook plugin (v1.2+) then you can use the configuration in config-examples for an example of a simple grub mkconfig hook on kernel updates
For anything else there will be more documentation in the near future that will explain eplug in more depth