Break the fs package up into smaller parts.

The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.

The new code layout is documented in CONTRIBUTING.

fs/log/redirect_stderr.go

@@ -0,0 +1,16 @@
+// Log the panic to the log file - for oses which can't do this
+
+// +build !windows,!darwin,!dragonfly,!freebsd,!linux,!nacl,!netbsd,!openbsd
+
+package log
+
+import (
+	"os"
+
+	"github.com/ncw/rclone/fs"
+)
+
+// redirectStderr to the file passed in
+func redirectStderr(f *os.File) {
+	fs.Errorf(nil, "Can't redirect stderr to file")
+}