Scheduled close event for thread save to config vars

[Taaku18]

According to Automatic dyno restarts, all dynos will restart at least once every 27 hours.

Dynos are also restarted (cycled) at least once per day to help maintain the health of applications running on Heroku. Any changes to the local filesystem will be deleted. The cycling happens once every 24 hours (plus up to 216 random minutes, to prevent every dyno for an application from restarting at the same time).

During this period, local caches are deleted, which results in the inability to set the scheduled closure time to longer than 24 hours.

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This PR resolves this issue.

Fixes #134

• Use call_later() instead of sleep() for scheduling.
• Created a new internal config var: closures.
• Bot:
  • loads closures upon start
  • removes closures['id'] upon deletion

Format:

'closures': {
    'recipient_id': {
        'time': 'ISO 8601 time string',
        'closer_id': int,
        'silent': bool,
        'delete_channel': bool,
        'message': 'message string'
    },
    ...
}

• recipient_id (str) the id of the recipient, aka thread.id.
• time (str) an 'ISO 8601 formatted datetime string.
• closer_id (int) the user who initiated the closure of the thread.

The following are the same as the parameters of the close() function.

• silent (bool)
• delete_channel (bool)
• message (str)

Unresolved Known Issues

• During the bot's downtime (when bot restarts), messages during this period are ignored. Therefore the close schedule will not terminate.

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Aside

#Addresses #133

• Improved formatting in core/config.py

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Please carefully review this PR and minor version bump upon approval.

[kyb3r]

Update changelog, increment minor patch version, and then I will merge.

[Taaku18]

Update changelog, increment minor patch version, and then I will merge.

Ready to merge.