sendSimpleMessage should accept SendSimpleMessageOptions

[zmarkan]

What?

At the moment sendSimpleMessage accepts SendMessageOptions, which takes an optional attachment: AttachmentOptions property.

This is incorrect for sending simple, text-only messages, and will appear as a suggestion in VSCode and other IDEs that support TS typings.

Suggested improvements

Create a new interface SendSimpleMessageOptions that doesn't include the attachment property.