✨ Add a merge subcommand

[jossmoff]

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• I have searched in the issues and found no similar issues.

Description

It could be useful to have a command that allows you to merge to stories. The use case would be if you have two events which are too granular you can then merge them together under a larger story

Solution

Command would look something like

bookshelf [STORY1] [STORY2] [NEWSTORY]

Pseudo code:

Both stories don't exists:
  throw exception
one of the stories is in progress:
  throw exception
merge each of the chapters
create a new story with those chapter 
save the new story
delete the other stories

Are you willing to submit PR?

• Yes I am willing to submit a PR!