Happy new year 2021!

• Issue #79: Python 3.9 support
• Issue #74: Help on dependency issues
• Issue #70: Document streamable file types
• Issue #68: Silence hachoir warnings ([warn] [/file[0]/uid] ...)
• Issue #65: Custom Thumbnail For the Files getting Uploaded
• Issue #43: Write tests
• Issue #40: Not using system HTTP Proxy
• Issue #38: Upload to Pypi using Github Actions
• Issue #36: Database is locked
• Issue #35: Document send files to a chat_id
• Issue #13: Change session directory enhancement
• Issue #11: Change session directory enhancement
• Issue #3: Split large files (> 2GB)