[go.py] Additional key bindings for increased usability

[mkoskar]

I propose to have following additional key bindings while inside go.py matching mode:

• Ctrl-N – next entry (equivalent of Tab)
• Ctrl-P – previous entry (equivalent of Shift-Tab)
• Esc, Ctrl-C, Ctrl-G – cancel go.py

Rationale:

All of the above but mainly Ctrl-N, Ctrl-P are often used in go.py-like interfaces (e.g., dmenu, Ctrl-P, etc.). Also it is frequently desirable to cancel go.py and get back without doing anything.