[hacc] Don't recurse prepare and finish if they've been manually defined.
[hacc] Document needed a custom fill function after all
[hacc] Refactor hacc/test/files.t.cpp a bit
[hacc] Add filey functions to documents.t.cpp
[hacc] Add File::rename (untested)
[hacc] Test saved document
[hacc] Clobber before writing to file in documents.t.cpp
[various] Manually recurse finishing because hacc doesn't any more