Only download content of the channels the user is following

[asmaier]

I know I can restrict the download to a list of channels, but I have to manually maintain that list.
Therefor it would be nice to have an option to only download data from the slack channels my user is following at the moment and not every public channel. Would this be possible to do?

[jcul]

I just submitted pull request #21 which adds option --excludeNonMember to do this.