Fetching only starred and/or reacted items

[rusq]

Is your feature request related to a problem? Please describe.
Some people organise their information using stars and reactions. Currently there's no way to get only the starred and/or reacted items, and this might be a problem on a large workspaces, when the only choice would be to manually assemble the list of items to download, or download the large workspace in full.

Describe the solution you'd like
Implement the ability to export only starred and/or reacted items (messages, replies, attachments)

Describe alternatives you've considered
Getting with curl and assembling list manually.

Additional context
Fork from #109

[mootari]

What about context? E.g., if the filter targets a reply, should there be an option to also save the thread up until that point (or alternatively the initial message)?

[rusq]

As I remember every time that conversation.reply is called, even with next cursor, it always returns the first message of the thread, as the first item in the response messages. It would make sense to fetch prior messages, between the first message, and the thread reply returned by the "starred" items request.

[rusq]

#219

Is your feature request related to a problem? Please describe.
Many people use Slack's save feature to organize messages.

Describe the solution you'd like
Implement the ability to export only saved items (messages, replies, attachments). Slack's export includes "is_starred": true, for saved items. A similar feature would be really helpful, and/or the ability to export only saved messages to one file.