If we rip out embedded images from raw_content then mark them as
pyfed:inlineImage. Receiving side will know then that those
attachments are included as inline images should they wish to
exclude those, if they support inline images via markdown or html.
Also rip out all embedded images, not just the ones from the
senders domain.
Maps to a `DiasporaReshare` for the Diaspora protocol.
The `Share` entity supports all the properties that a Diaspora reshare does. Additionally two other properties are supported: `raw_content` and `entity_type`. The former can be used for a "quoted share" case where the sharer adds their own note to the share. The latter can be used to reference the type of object that was shared, to help the receiver, if it is not sharing a `Post` entity. The value must be a base entity class name.
Closes#94