all: Refactor cmd/syncthing creating lib/syncthing (ref #4085) (#5805)

* add skeleton for lib/syncthing

* copy syncthingMain to lib/syncthing (verbatim)

* Remove code to deduplicate copies of syncthingMain

* fix simple build errors

* move stuff from main to syncthing with minimal mod

* merge runtime options

* actually use syncthing.App

* pass io.writer to lib/syncthing for auditing

* get rid of env stuff in lib/syncthing

* add .Error() and comments

* review: Remove fs interactions from lib

* and go 1.13 happened

* utility functions

lib/syncthing/cpuusage_windows.go

@@ -0,0 +1,27 @@
+// Copyright (C) 2014 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//+build windows
+
+package syncthing
+
+import "syscall"
+import "time"
+
+func cpuUsage() time.Duration {
+	handle, err := syscall.GetCurrentProcess()
+	if err != nil {
+		return 0
+	}
+	defer syscall.CloseHandle(handle)
+
+	var ctime, etime, ktime, utime syscall.Filetime
+	if err := syscall.GetProcessTimes(handle, &ctime, &etime, &ktime, &utime); err != nil {
+		return 0
+	}
+
+	return time.Duration(ktime.Nanoseconds() + utime.Nanoseconds())
+}