Api change

[dougthor42]

This changes the API: get and add are no longer used and are instead replaced with data. This will make it so that I can eventually implement #29.

# old
GET /api/v1/get/<metric_name>
POST /api/v1/add   {json_data}

# new
GET /api/v1/data/<metric_name>    # to get data for a specific metric
POST /api/v1/data   {json_data}

Also a cleanup of add_data.sh even though that's kinda out of scope of this MR. Oops.