AbsolutePath returns the absolute path.

DownloadFile downloads a file.

ExpandPath expands tilde '~' character for home.

GetFileName returns file name from URL.

HTTPClient returns a new HTTP client.

PasswordPrompt prompts user for a password (hiding it's value from console).

ShaHash calculates hash from io.Reader content.

UnpackTarGZ unpacks .tar.gz file to destDir.

ValidateFileIntegrity validates down.