Adds Command#sort_by_creation
Adds events to issues in Show
Doesn't listen to unimportant events - for now
Handles paging of events
Gets comments and events multi-threaded

Comments and events can be fetched in parallel to avoid blocking the
program during the HTTP GET requests.
Fix handling of unimportant events in Formatting

We cannot return an empty string, as it leads to unwanted newlines in
the output. The guarding logic is also moved out of format_event, as
the responsibility to handle this is better placed inside of
format_comments_and_events.
Merge pull request #155 from LFDM/events

Events and issues