feature suggestion: provide xmenu as a library

[sewnie]

this can be useful for https://github.com/phillbush/ctrlmenu and https://github.com/phillbush/xfiles

[phillbush]

That is in my TODO list, but it is not a simple change to do.

I want to work on xmenu further, improving it with the experience I gained in that side project, ctrlmenu, which is related to xmenu and provides kinda the same thing, but differently.

That can be done in the (not near) future tho.