Basic rate limiting implementation.

Added `--limit-upload` and `--limit-download` flags to rate limit
backups and restores.

vendor/github.com/pkg/sftp/sftp.go

@@ -1,5 +1,5 @@
 // Package sftp implements the SSH File Transfer Protocol as described in
-// https://filezilla-project.org/specs/draft-ietf-secsh-filexfer-02.txt
+// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
 package sftp
 
 import (