Utility to backup files using .NET core.

Features:

• Save last 3 copies of each file in directory beside
• SFTP support using SSH.NET
• Simple JSON file based configuration
• Skip non-changed files
• Fast implementation based on async operations (partially)

Limitations and ways of extension:

• Support only password auth for SFTP
• Don't support ignore lists
• Not designed to backup really large files, can raise out of memory
• Need resource utilization controls