CurseFetch

## `download`

Download the modpack file from the curseforge.

- `--out`: the destination of the output, can be either a file or a directory
- `--unzip`: extract the compressed archive if capable to the given directory; or raise an exception if not capable.
- `--current-version`: the file id of the current version to check if there's a need to update; or a path to a text file that contains the previous content.
