Shorten MetaGraph representation

[huguesmp]

This is an attempt to address #63.

It is also my first PR, and I'm not very experienfed with Julia, so any advice is welcome :)

[henrik-wolf]

Thank you for preparing this. I believe in this case it does not really matter, but it might be cleaner to get the type of the graph similar to how we get the type of the Label, VertexData... like this:

function Base.show(
    io::IO, meta_graph::MetaGraph{<:Any, BaseGraph, Label, VertexData, EdgeData}
) where {BaseGraph, Label, VertexData, EdgeData}
    print(...)
end

some documentation for this pattern

Secondly, the problem with printing a lot still persists when I put something really big as the label:

julia> mg = MetaGraph(g1, [i=>i for i in 1:100], [(src(e), dst(e))=>1 for e in edges(g1)], g1)

But I think we can just say that is not the intended use?

[codecov]

Codecov Report

Merging #64 (ad09111) into master (5c98f33) will not change coverage.
The diff coverage is n/a.

❗ Current head ad09111 differs from pull request most recent head 407a3a2. Consider uploading reports for the commit 407a3a2 to get more accurate results

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Files Changed	Coverage Δ
src/metagraph.jl	90.24% <ø> (ø)

[huguesmp]

I changed the code to follow the pattern you describe (of which I was unaware, thank you :), it is indeed much cleaner and more in line with the rest of the code.

As for the graph data question, I always figured it was only meant for a title for the graph (that's what I've been using it for), but it's true that there is no restriction on what one can put there.

Maybe someone can chime in on what the intention is with that field.

[gdalle]

I agree that graph data is not meant to scale with $|V|$ or $|E|$, otherwise it would be in the vertex and edge data. So I think this fix is fine, thank you!