Adjust to API changes regarding the `content` key
In one of the recent changes in the TextAPI, users are allowed to provide more than one
content for an Item. This has been solved by adding an array of Content Objects which each hold a URL to a serialization/version of the Item.
An example is provided in the respective section.
TIDO has to adjust to this change. Also, users are free to choose the value of the MIME type parameter; while only the key of said parameter is defined (
type), users can freely choose its value, differentiating e.g. several HTML serializations of an Item.