Add DELETE verb to API calls

[veekaybee]

Description

The gitfeed server is tiny and runs into performance issues at query-time, even after some tuning. We've added DB indexes for performance tuning, but also dding DELETE will enable clients to delete post records from the DB particularly since we only care about state for the last 10 posts collected over an hour and don't want to keep state or data for this particular application.

Steps

1. Implement auth so only clients with tokens can delete resources from API
2. Implement DELETE endpoint for all posts/posts for a given number of ID

Intermediate solution: cron script to delete the database/clear out last n entries every x hours.

[veekaybee]

Addressed partially by #6