Major changes to how proximity works.

Hi,

I liked the basic approach you took with proximity, but I wanted something even simpler: a way to watch the current directory and execute a command if anything changed. So I did some surgery to simplify proximity for users.

This may not be a change you want to accept. I totally understand if that's the case. If so, I hope you don't mind, but I will probably rename my fork to something else (with reference to it being based heavily on proximity) since it fulfills my needs.

Let me know what you think.