total revenue generated in the whole system over a start/end date range

[marlitas]

This endpoint should return the total revenue across all merchants between the given dates, inclusive of the start and end date.

The URI should follow this pattern: GET /api/v1/revenue?start_date=<start_date>&end_date=<end_date>

Assume your users will only send dates in the format YYYY-MM-DD. Revenue must be counted for any invoices on the end_date as well.

An error should be returned if either/both the start date or end date are not provided.

Example JSON response for GET /api/v1/revenue?start=2012-03-09&end=2012-03-24

{
"data": {
"id": null,
"attributes": {
"revenue" : 43201227.8000003
}
}
}