Add the ability to obtain the manifest

[Kenny164]

Use the --project argument to pass the modpack's ID and download
the zipfile from curse and use it's included manifest.json.

This will create a temporary directory for the output for now and
will print the directory to the user at the end of execution.

e.g. downloader.py --project 242462 will get all the mods (at this time of writing).

Apologies in advance for my code (it's been a while) and I'm not well versed in PRs nor python. This is more for advice about what I'm wanting to add on the long term.

I'm planning a couple more features such as:

• Update an existing MultiMC instance
  • find relevant folders (where multimc has the instances, etc)
  • copy an existing instance (if specified as an argument) or create one
  • update the instance.cfg
  • Sync configs and mods (probably just a remove all and re-populate)
• Download forge according to the version stated in the manifest

At what point should I consider a new .py file and import your doDownload() function?

Thanks for creating this, making it available and your time.

[wassname]

I'm don't have merge rights but I thought I would help by reviewing this.

Curse has since changed the pack_base_url so it doesn't work now, but it will if you update it to:

pack_base_url = 'https://minecraft.curseforge.com/projects/%s/files/latest' % project_id

Other than that the code works for me, and looks good, thanks Kenny164. I reckon you should merge it after that change.