* chain/src/item/default/mod.rs:
* graph/src/labelled/binary.rs:
* graph/src/labelled/double.rs:
* graph/src/lib.rs: If we set the option "ordering" to be "out" in the
  declaration of nodes at the beginning, then GraphViz will not change
  the order of children out of nodes.  This is much better looking in
  my opinion.

* INSTALL: make insists in changing this file, so let it be.

Now the binding part is finished.

What remains is a bug encountered when planting a fragment to the
forest which intersects a packed node, which would lead to invalid
forests.  This will also cause problem when planting a packed
fragment, but until now my testing grammars do not produce packed
fragments, so this problem is not encountered yet.

I am still figuring out efficient ways to solve this problem.

I should have staged and committed these changes separately, but I am
too lazy to deal with that.

The main changes in this commit are that I added the derive macro that
automates the delegation of the Graph trait.  This saves a lot of
boiler-plate codes.

The second main change, perhaps the most important one, is that I
found and tried to fix a bug that caused duplication of nodes.  The
bug arises from splitting or cloning a node multiple times, and
immediately planting the same fragment under the new "sploned" node.
That is, when we try to splone the node again, we found that we need
to splone, because the node that was created by the same sploning
process now has a different label because of the planting of the
fragment.  Then after the sploning, we plant the fragment again.  This
makes the newly sploned node have the same label (except for the clone
index) and the same children as the node that was sploned and planted
in the previous rounds.

The fix is to check for the existence of a node that has the same set
of children as the about-to-be-sploned node, except for the last one,
which contains the about-to-be-planted fragment as a prefix.  If that
is the case, treat it as an already existing node, so that we do not
have to splone the node again.

This is consistent with the principle to not create what we do not
need.

I decide to adopt a new approach of recording and updating item
derivation forests.  Since this affects a lot of things, I decide to
commit before the refactor, so that I can create a branch for that
refactor.

I need more than the ability to clone nodes: I also need to split the
nodes.  Now this seems to be correctly added.

Finally the prototype parser has produced the first correct forest.
It is my first time to generate a correct forest, in fact, ever since
the beginning of this project.

It seems to be complete now, but still awaits more tests to see where
the errors are, which should be plenty, haha.

Now the forest can detect if a node is packed or cloned, and correctly
clones a node in those circumstances.  But it still needs to be
tested.

I have an ostensibly working prototype now.

Further tests are needed to make sure that the algorithm meets the
time complexity requirement, though.

I seem to have finished the implementation of forests.  Now it remains
the implementation of the chain-rule machine, of which I have a rough
plan now.