Add support for reverse edge filters

[drkameleon]

Let's take the famous sample11.art.

So..., we have a graph with actors, where they are from, which countries they have acted in, etc.

Right now, to get e.g. the Person(s?) that has directed the Movie with the title "Mystic River" we could perform the following query:

And the results are the ones we'd expect.

Now, given that directed is an edge that goes from a Person ➡ to a Movie, querying like this is fine.

But what if we want the reverse thing? For example: find the Movie's that were directed by a given Person?

One way would be to make the edge bi-directional (in a few words: "Mystic River" pointing ➡ to Eastwoord and Eastwood pointing back ⬅️ to "Mystic River"). But that completely defeats the purpose of having direction-aware edges and the meaningfulness of it all.

So, basically, right now, there is simply no way to - elegantly - perform this type of seemingly ultra-logical query.

So? Let's find a way! 🚀

[drkameleon]

And... 💣 :

It worked! 😄 🚀

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For future reference, the way to make it work like that (reverse an edge filter) - at least for now:

• |> normal direction (same as not using it all)
• <| reverse direction
• <|> any direction

[drkameleon]

Ready to merge! 🚀