Utility for downloading files from Mattermost.

Mattermost (MM) gives URLs for file downloading like
https://MACHINE/api/v4/files/FILE
and you can not download it with simple fetch/curl/wget.
That utility uses MM's API to download it.

    $ mmfileget https://MACHINE/api/v4/files/FILE
    Name: Some filename.jpg
    Type: image/jpeg
    Size: 43713
    Download? Ctrl-D/C

Press Ctrl-D to allow file download under provided name.
Press Ctrl-C to quit program.

    $ mmfileget https://MACHINE/api/v4/files/FILE TARGET-NAME

will download file and save it in TARGET-NAME file.

It uses ~/.netrc file (single line per machine format) for finding
authentication credentials for MACHINE. You can override it with NETRC
environment variable.