Create Announcements Endpoints

[ben9583]

We should the following endpoints for announcements:

• /announcements/metadata/{id}: Gets the metadata for the announcement id (date, title, blurb)
• /announcements/get/{id}: Gets the markdown content for the announcement id
• /announcements/last: Returns the ID of the most recent announcement
• /announcements/last/{num}: Returns the sorted IDs of the num most recent announcements (must cap num to something)

The API should make use an ocflib backend tool to get this information, rather than directly obtaining the information from the repository itself. These functions should essentially just be interfaces for the respective ocflib functions that get this information (maybe /last can use the same ocflib method as /last/{num}, but withnum = 1). It should be assumed that ocflib implements an appropriate caching strategy.