Split off GraphViz

See graphp/graphviz#1

Author: clue

README.md

@@ -85,11 +85,11 @@ The recommended way to install this library is [through composer](http://getcomp
 ```
 
 Optional recommendation:
+
 In order to be able to use the [graph drawing feature](#graph-drawing) you'll have to
-install GraphViz (`dot` executable). Users of Debian/Ubuntu-based distributions may simply
-invoke `sudo apt-get install graphviz`, Windows users have to
-[download GraphViZ for Windows](http://www.graphviz.org/Download_windows.php) and remaining
-users should install from [GraphViz homepage](http://www.graphviz.org/Download.php).
+install the [graphp/graphviz](https://github.com/graphp/graphviz) package and GraphViz itself (`dot` executable).
+
+See [graphp/graphviz](https://github.com/graphp/graphviz) for details.
 
 ## Tests
 

composer.json

@@ -2,7 +2,7 @@
     "name": "clue/graph",
     "type": "library",
     "description": "A mathematical graph/network library written in PHP",
-    "keywords": ["graph", "network", "mathematical", "graphviz", "vertex", "edge", "shortest path", "dijkstra", "moore-bellman-ford", "minimum spanning tree", "kruskal", "prim"],
+    "keywords": ["graph", "network", "mathematical", "vertex", "edge", "shortest path", "dijkstra", "moore-bellman-ford", "minimum spanning tree", "kruskal", "prim"],
     "homepage": "https://github.com/clue/graph",
     "license": "MIT",
     "autoload": {
@@ -13,5 +13,8 @@
     },
     "require-dev": {
         "phpunit/phpunit": "3.7.* | ~4.0"
+    },
+    "suggest": {
+        "graphp/graphviz": "GraphViz graph drawing / DOT output"
     }
 }