Compact print of GNNGraphs

[aurorarossi]

Implementation of the format proposed in issue #169.
Example:

julia> [ rand_graph(10,20),
         rand_graph(10,20, ndata=(a=rand(5,10),)),
         rand_graph(10,20, ndata=rand(5,10), edata=rand(2,20), gdata=rand(1,1)),
         rand_graph(10,20, ndata=(a=rand(5,10), b=rand(3,10)), edata=rand(2,20))]

        4-element Vector{GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}}}:
         GNNGraph(10, 20) with no data
         GNNGraph(10, 20) with a: 5×10 data
         GNNGraph(10, 20) with x: 5×10, e: 2×20, u: 1×1 data
         GNNGraph(10, 20) with (a: 5×10, b: 3×10), e: 2×20 data

[CarloLucibello]

A couple of problems I noticed:

# ndata and edata too indented
julia> g = rand_graph(10, 20, ndata=rand(10), edata=(e=rand(2,20),w=rand(2,20)))
GNNGraph:
  num_nodes = 10
  num_edges = 20
    ndata:
        x => 10-element Vector{Float64}
    edata:
        e => 2×20 Matrix{Float64}
        w => 2×20 Matrix{Float64}

# error
julia> [g,g,g]
3-element Vector{GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}}}:
Error showing value of type Vector{GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}}}:
ERROR: BoundsError: attempt to access Tuple{Int64} at index [2]
Stacktrace:
  [1] getindex(t::Tuple, i::Int64)
    @ Base ./tuple.jl:29
  [2] print_feature(io::IOContext{IOBuffer}, feature::NamedTuple{(:x,), Tuple{Vector{Float64}}})
    @ GraphNeuralNetworks.GNNGraphs ~/.julia/dev/GraphNeuralNetworks/src/GNNGraphs/gnngraph.jl:227
  [3] print_all_features(io::IOContext{IOBuffer}, feat1::NamedTuple{(:x,), Tuple{Vector{Float64}}}, feat2::NamedTuple{(:e, :w), Tuple{Matrix{Float64}, Matrix{Float64}}}, feat3::NamedTuple{(), Tuple{}})
    @ GraphNeuralNetworks.GNNGraphs ~/.julia/dev/GraphNeuralNetworks/src/GNNGraphs/gnngraph.jl:245
  [4] show(io::IOContext{IOBuffer}, g::GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}})
    @ GraphNeuralNetworks.GNNGraphs ~/.julia/dev/GraphNeuralNetworks/src/GNNGraphs/gnngraph.jl:261
  [5] sprint(f::Function, args::GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}}; context::IOContext{Base.TTY}, sizehint::Int64)
    @ Base ./strings/io.jl:112
  [6] alignment_from_show(io::IOContext{Base.TTY}, x::GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}})
    @ Base ./show.jl:2719
  [7] alignment(io::IOContext{Base.TTY}, x::GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}})
    @ Base ./show.jl:2738
  [8] alignment(io::IOContext{Base.TTY}, X::AbstractVecOrMat, rows::Vector{Int64}, cols::Vector{Int64}, cols_if_complete::Int64, cols_otherwise::Int64, sep::Int64, ncols::Int64)
    @ Base ./arrayshow.jl:69
  [9] _print_matrix(io::IOContext{Base.TTY}, X::AbstractVecOrMat, pre::String, sep::String, post::String, hdots::String, vdots::String, ddots::String, hmod::Int64, vmod::Int64, rowsA::UnitRange{Int64}, colsA::UnitRange{Int64})
    @ Base ./arrayshow.jl:207
 [10] print_matrix(io::IOContext{Base.TTY}, X::Vector{GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}}}, pre::String, sep::String, post::String, hdots::String, vdots::String, ddots::String, hmod::Int64, vmod::Int64) (repeats 2 times)
    @ Base ./arrayshow.jl:171
 [11] print_array
    @ ./arrayshow.jl:358 [inlined]
 [12] show(io::IOContext{Base.TTY}, #unused#::MIME{Symbol("text/plain")}, X::Vector{GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}}})
    @ Base ./arrayshow.jl:399
 [13] (::REPL.var"#43#44"{REPL.REPLDisplay{REPL.LineEditREPL}, MIME{Symbol("text/plain")}, Base.RefValue{Any}})(io::Any)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:267
 [14] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:521
 [15] display(d::REPL.REPLDisplay, mime::MIME{Symbol("text/plain")}, x::Any)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:260
 [16] display(d::REPL.REPLDisplay, x::Any)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:272
 [17] display(x::Any)
    @ Base.Multimedia ./multimedia.jl:328
 [18] #invokelatest#2
    @ ./essentials.jl:729 [inlined]
 [19] invokelatest
    @ ./essentials.jl:726 [inlined]
 [20] print_response(errio::IO, response::Any, show_value::Bool, have_color::Bool, specialdisplay::Union{Nothing, AbstractDisplay})
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:296
 [21] (::REPL.var"#45#46"{REPL.LineEditREPL, Pair{Any, Bool}, Bool, Bool})(io::Any)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:278
 [22] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:521
 [23] print_response(repl::REPL.AbstractREPL, response::Any, show_value::Bool, have_color::Bool)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:276
 [24] (::REPL.var"#do_respond#66"{Bool, Bool, REPL.var"#77#87"{REPL.LineEditREPL, REPL.REPLHistoryProvider}, REPL.LineEditREPL, REPL.LineEdit.Prompt})(s::REPL.LineEdit.MIState, buf::Any, ok::Bool)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:857
 [25] #invokelatest#2
    @ ./essentials.jl:729 [inlined]
 [26] invokelatest
    @ ./essentials.jl:726 [inlined]
 [27] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
    @ REPL.LineEdit ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/LineEdit.jl:2510
 [28] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
    @ REPL ~/.julia/juliaup/julia-1.8.3+0.aarch64/share/julia/stdlib/v1.8/REPL/src/REPL.jl:1248
 [29] (::REPL.var"#49#54"{REPL.LineEditREPL, REPL.REPLBackendRef})()
    @ REPL ./task.jl:484

# this is fine
julia> [ rand_graph(10,20),
                rand_graph(10,20, ndata=(a=rand(5,10),)),
                rand_graph(10,20, ndata=rand(5,10), edata=rand(2,20), gdata=rand(1,1)),
                rand_graph(10,20, ndata=(a=rand(5,10), b=rand(3,10)), edata=rand(2,20))]
4-element Vector{GNNGraph{Tuple{Vector{Int64}, Vector{Int64}, Nothing}}}:
 GNNGraph(10, 20) with no data
 GNNGraph(10, 20) with a: 5×10 data
 GNNGraph(10, 20) with x: 5×10, e: 2×20, u: 1×1 data
 GNNGraph(10, 20) with (a: 5×10, b: 3×10), e: 2×20 data

[CarloLucibello]

Needs also a git --rebase -i origin/master.

[CarloLucibello]

there are a lot of unrelated code formatting changes in this PR. It is fine and you can keep them, but for the future, these changes should be done in a separate PR since they make it harder to review the actual changes in the PR.