Export data options

[Mozzo1000]

Besides having the API available and (soon documented #7) - a few pre-configured ways to download your own data should be available.
The data would be your books and their accompanying metadata (reading status, isbn, pages etc) and notes.

Proposed export options:

• CSV
• JSON
• HTML

If you are hosting your own server you of course have full access to the database and can get the data out that way but if you are using a shared server and/or need a simpler way to get your data these options should work well as compliments.

[Mozzo1000]

To begin adding exporting of data. I would like this to run in the background instead of the API servers main thread, work on background tasks have started see Background tasks.

This work on background tasks will also be applicable to importing data, see #9

[Mozzo1000]

The basic framework for background tasks has been added in commits 61304b0, f8ba8d1, be5fc60, 9c537b5 and 38de327

There is also now a CSV export worker. The worker will create a csv files containing all the users books. The user can then download the file on demand.

[Mozzo1000]

Note, the CSV export worker that was added in d1cbb0c currently has no failsafes and will crash if there is an error.

[Mozzo1000]

JSON export option has been added in commit 817f08e