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.
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors