Support extending Vertex by registering to Graph within its ctor
Add tests for explicit Vertex instantiation
Support extending Edge by registering to its vertices within ctor
Swap Vertex ctor $graph and $id attributes

A Vertex can not exist without a Graph instance
Merge branch 'master' into add-extend

Conflicts:
	lib/Fhaculty/Graph/Graph.php
Add extension support to CHANGELOG
Merge pull request #82 from clue/add-extend

Support extending Graph, Vertex and Edge