Create ocflib Tools for Announcements

[ben9583]

We'll use ocflib to get information on announcements, which the API will call as an interface between the user and our backend. ocflib should support the following specifications:

• Get metadata for a post #51
• Get content for a post
• Get the IDs for the last num posts

These implementations should make use of the GitHub API to find and retrieve the file contents of a given announcement. They should also make use of caching so we don't have to do this often (see other ocflib projects for specific details).