fd integration?

[kyoheiu]

A while ago I thought about this, and decided not necessary. Today I felt it'd be better to have this, so will give it a try.

• How to integrate? -> AFAIK fd does not expose internal api, so a kind of dirty hack may be needed. (Such as just re-using stdout, etc)
• How to manage the state? -> Thanks to the refactoring, chdir can catch the directory change, so it may reset the fd state.
• How to display the result? -> Each result path have to be shorten. If necessary, use full screen?