`CpMenu` doesn't need to be a global

[mrjones2014]

Instead, cpmenu should be it's own Lua module, and since Lua modules are cached, once you mutate it, requireing it again will give the mutated value.

Then the main module should provide a setup function which sets the CpMenu.

This way you can also set it up as a proper telescope extension so that it can be configured in a user's Telescope configuration.

I'll work on a PR for this.