Quick Switch over 9 windows

Repeated 'q' command shows next window numbers when there're over 9
windows.
Window Search Switching

Press '/' in command mode and enter search keyword for window title to
switch. The command 'n' and 'N' also works for forward/backward
searching.
Merge branch 'window_search_switching' of https://github.com/inkyfox/Vimdow
Fixed infinite loop when search failed