| path | Path to file to be written. |
| append | When true, appends data to the given file instead of overwriting. |
Creates a new instance and a file on disk where downloaded data will be written to.
Throws an ArgumentException if a file cannot be created. If a path to a file in a non-existent directory is given, all required directories are created. If a file exists, it will be overwritten, unless in append mode. If a file doesn't exist, it is created regardless of append flag.