Fixes #51 Open file in last active window
Fixes #48 Select Up dir + Down + siblings

Key bindings have been chosen arbitrarily to
U, D, S and s
Merge pull request #60 from syl20bnr/fixes_51

Fixes #51 Open file in last active window
Merge pull request #64 from syl20bnr/Fixes_48_go_up_down_node

Fixes #48 Select Up dir + Down + siblings