Prepare for termbox/windows build

`TAGS=termbox make` (or `go build -tags termbox`)

src/terminal_unix.go

@@ -0,0 +1,13 @@
+// +build !windows
+
+package fzf
+
+import (
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+func notifyOnResize(resizeChan chan<- os.Signal) {
+	signal.Notify(resizeChan, syscall.SIGWINCH)
+}