crecord: add `content` properties to all nodes
In order to have a unified API of what can be searched, let's provide
a `content` property to each node type. This way we can search
filenames, context headers (e.g. containing function names, if
deducible from patch context) or changed lines themselves.
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true