make clipboard(g) work (#121)

Author: anandijain

src/SimpleGraphs/SimpleGraphs.jl

@@ -50,7 +50,7 @@ An abstract type representing a simple graph structure.
 """
 abstract type AbstractSimpleGraph{T<:Integer} <: AbstractGraph{T} end
 
-function show(io::IO, g::AbstractSimpleGraph{T}) where T
+function show(io::IO, ::MIME"text/plain", g::AbstractSimpleGraph{T}) where T
     dir = is_directed(g) ? "directed" : "undirected"
     print(io, "{$(nv(g)), $(ne(g))} $dir simple $T graph")
 end

test/simplegraphs/simplegraphs.jl

@@ -30,16 +30,18 @@ import Random
     gx = SimpleGraph()
     for g in testgraphs(gx)
         T = eltype(g)
-        @test sprint(show, g) == "{0, 0} undirected simple $T graph"
+        @test repr("text/plain", g) == "{0, 0} undirected simple $T graph"
         @test @inferred(add_vertices!(g, 5) == 5)
-        @test sprint(show, g) == "{5, 0} undirected simple $T graph"
+        @test repr("text/plain", g) == "{5, 0} undirected simple $T graph"
+        @test eval(Meta.parse(repr(g))) == g
     end
     gx = SimpleDiGraph()
     for g in testdigraphs(gx)
         T = eltype(g)
-        @test sprint(show, g) == "{0, 0} directed simple $T graph"
+        @test repr("text/plain", g) == "{0, 0} directed simple $T graph"
         @test @inferred(add_vertices!(g, 5) == 5)
-        @test sprint(show, g) == "{5, 0} directed simple $T graph"
+        @test repr("text/plain", g) == "{5, 0} directed simple $T graph"
+        @test eval(Meta.parse(repr(g))) == g
     end
 
     gx = path_graph(4)