Support `POST direct_messages/events/new`

[amachino]

https://developer.twitter.com/en/docs/direct-messages/sending-and-receiving/api-reference/new-event

Requires a JSON POST body and Content-Type header to be set to application/json. Setting Content-Length may also be required if it is not automatically.

[teifip]

@Mach I have just created pull request #278. Let's see if it is accepted, or at least used as the basis to move forward on this issue.

[peterpme]

@Mach, @teifip supporting this in: https://github.com/Preposterous/twitter-lite