Use LightGraphs instead of Graphs in README.md

This readme still used mostly Graphs.jl instead of LightGraphs.jl. As
the former package is deprecated and GraphPlots.jl does not work with it
anymore, every occurrence of Graphs has changed to LightGraphs.

Some functions functions such as num_vertices or out_degree had to be
changed for that.

Author: simonschoelly

README.md

@@ -33,8 +33,8 @@ gplot(g)
 
 ## Add node label
 ```julia
-using Graphs
-nodelabel = [1:num_vertices(g)]
+using LightGraphs
+nodelabel = [1:nv(g)]
 gplot(g, nodelabel=nodelabel)
 
 ```
@@ -47,7 +47,7 @@ gplot(g, nodelabel=nodelabel, nodelabeldist=1.5, nodelabelangleoffset=π/4)
 ## Control the node size
 ```julia
 # nodes size proportional to their degree
-nodesize = [Graphs.out_degree(v, g) for v in Graphs.vertices(g)]
+nodesize = [LightGraphs.out_degree(g, v) for v in LightGraphs.vertices(g)]
 gplot(g, nodesize=nodesize)
 ```
 
@@ -57,7 +57,7 @@ Feed the keyword argument `nodefillc` a color array, ensure each node has a colo
 using Colors
 
 # Generate n maximally distinguishable colors in LCHab space.
-nodefillc = distinguishable_colors(num_vertices(g), colorant"blue")
+nodefillc = distinguishable_colors(nv(g), colorant"blue")
 gplot(g, nodefillc=nodefillc, nodelabel=nodelabel, nodelabeldist=1.8, nodelabelangleoffset=π/4)
 ```
 
@@ -76,13 +76,13 @@ gplot(g, nodelabelsize=nodelabelsize, nodesize=nodesize, nodelabel=nodelabel)
 
 ## Draw edge labels
 ```julia
-edgelabel = [1:Graphs.num_edges(g)]
+edgelabel = [1:LightGraphs.ne(g)]
 gplot(g, edgelabel=edgelabel, nodelabel=nodelabel)
 ```
 
 ## Adjust edge labels
 ```julia
-edgelabel = [1:Graphs.num_edges(g)]
+edgelabel = [1:LightGraphs.ne(g)]
 gplot(g, edgelabel=edgelabel, nodelabel=nodelabel, edgelabeldistx=0.5, edgelabeldisty=0.5)
 ```
 
@@ -122,7 +122,7 @@ gplot(g, layout=spectral_layout)
 ```julia
 nlist = Array(Vector{Int}, 2) # two shells
 nlist[1] = [1:5] # first shell
-nlist[2] = [6:num_vertices(g)] # second shell
+nlist[2] = [6:nv(g)] # second shell
 locs_x, locs_y = shell_layout(g, nlist)
 gplot(g, locs_x, locs_y, nodelabel=nodelabel)
 ```