Extend the API docs with a format for callback arguments

[joern]

Nearly every plugin and a lot of core methods use callbacks. The current documentation system (inline comments, parser etc.) don't provide a way to document the arguments for those callbacks, forcing the documenter to describe them in plain text format, which is not efficent and difficult to read.

A good (or rather bad) example are the various callbacks for Interface's drag plugin. While the several options are described (eg. Function onDrag ...), the arguments have to be described in plain text and are therefore often missing.

Enhancing the system would help both developers and users, as both writing and reading would be easier.

[john]

Fixed with the new API docs.