Add new Meeting Statuses to documentation and project

[bonfirefan]

In order to better track meetings, we will add RESCHEDULED and UPDATED as meeting statuses. Comes up in Issue #16 and in the general last-minute rescheduling of meetings.

RESCHEDULED means the meeting was moved to a new date UPDATED is the new meeting time of a meeting.

Statuses are now:

• CANCELLED
• TENTATIVE
• CONFIRMED
• PASSED
• RESCHEDULED
• UPDATED

We'll need to add Pittsburgh-specific documentation reflecting this.

[ben-nathanson]

We don't have Pittsburgh-specific docs yet, right? I could start it out in markdown and if we decide to do a website later we can port the contents over to HTML.

[bonfirefan]

I think this is a good idea, especially for onboarding

[bonfirefan]

The markdown docs already exist in the project!

[ben-nathanson]

Closed by PR #84