Add support for "204 No content" return when DELETE-ing data

[virtualtam]

Issue

See https://github.com/shaarli/Shaarli/pull/1141#issuecomment-395497664

When consuming an endpoint with an HTTP DELETE request, a 204 No content response is returned, with an empty body.

The client attempts to JSON-decode the response, which fails (unless the --format text flag is used).

Fix

Suggestion:

• check the HTTP return code
• expect a 204 response with an empty body for DELETE endpoints