Support searching in project files and swift packages.

[leo1mml]

First of all this is an awesome plugin.

Second: Is it possible to search for files/text inside the sub swift packages? It would be great to have a seamless integrated code navigation in neovim. I wonder if there's any peculiarity with local packages and remote ones inside derived data. I have no experience with making neovim plugins, so I'm unable to help. But I believe this feature would be great for people using this plug in.