create_event spec does not match documented parameters

[aandis]

As per this library, create_event expects -

      {
        :'event_name' => :'event_name',
        :'event_date' => :'event_date',
        :'identifiers' => :'identifiers',
        :'contact_properties' => :'contact_properties',
        :'event_properties' => :'event_properties'
      }

This is completely different from what's documeted at https://developers.brevo.com/docs/track-custom-events-rest

There are many such incosistencies reported by other users - #12, #10, #8

Overall, this appears to be a very poorly maintained library for paying Brevo customers. Please fix these issues.

[nicolasleger]

Also in the documentation #16