Refactor signal handling and Windows support

This commit drops webhook_windows.go in favor of simply pulling out the
signal handling code to separate files.

signals.go

@@ -0,0 +1,34 @@
+// +build !windows
+
+package main
+
+import (
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+func setupSignals() {
+	log.Printf("setting up os signal watcher\n")
+
+	signals = make(chan os.Signal, 1)
+	signal.Notify(signals, syscall.SIGUSR1)
+
+	go watchForSignals()
+}
+
+func watchForSignals() {
+	log.Println("os signal watcher ready")
+
+	for {
+		sig := <-signals
+		if sig == syscall.SIGUSR1 {
+			log.Println("caught USR1 signal")
+
+			reloadHooks()
+		} else {
+			log.Printf("caught unhandled signal %+v\n", sig)
+		}
+	}
+}