Merge markdown formatter into main sync chain

[MadBomber]

An enhancement I'd like to see is merging the jira-format-issue functionality with the main sync components so that I could do this:

jira-sync  <snip> update --markdown my_markdown_directory

My expectation of this new feature used in this way is that only those JIRA tickets that have been updated since the last time I did a sync would be passed into the formatter code. In the same way if the sync is to fetch-all with the --markdown option, then all JIRA tickets would be regenerated into my designated markdown directory.

The --custom-data-path option should also be available.