feat: Add config to enable instant file download

[artem-vavilov]

Issue: #66

[andrii-bodnar]

Hi @artem-vavilov, thanks for the contribution!

This download file functionality doesn't fit well into this API client, and it's something that's unique to this client. None of our other API clients have it, so I've even thought about removing it.

I'm not sure if it's a good idea to introduce the new config parameter, so I'd suggest changing the behavior a little bit.

Let's download the file only in cases when the destination parameter is specified. In that case, we'll still return the path to the downloaded file.

If the destination parameter is not passed - return the full API response.

For example, with the destination:

crowdin.download_file(file_id: your_file_id, destination: your_destination, project_id: your_project_id)

# -> should return the downloaded file path.

Without the destination:

crowdin.download_file(file_id: your_file_id, project_id: your_project_id)

# -> should return an object from the response

# {
#   "url": "https://production-enterprise-importer.downloads.crowdin.com/992000002/2/14.xliff?......",
#   "expireIn": "2019-09-20T10:31:21+00:00",
#   "etag": "ebd69a1b7e4c23e6d17891a491c94f832e0c82e4692dedb35a6cd1e624b62"
# }

Please let me know what you think about this!

[artem-vavilov]

If the destination parameter is not passed - return the full API response.

@andrii-bodnar I also considered this option but rejected it because it would dramatically change the behavior of some methods.

However, if you don't mind, I'm happy to implement this!

[andrii-bodnar]

@artem-vavilov yes, it could be a bit risky. We'll try to release it by adding a warning message to release notes about this change.

Could you please take a look at the #67 issue as well?

It would be great if we could address both of these issues within a single release.

[artem-vavilov]

New PR: #69