Add an API to access the entry contents from the browser as JSON

[elia]

This will allow frontend JS code to fetch and manipulate content with systems such as React.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It might be closed if no further activity occurs. Thank you for your contributions.