v0.8.0

• Feature: Add general purpose Attributes.
  (#103)
• BC break: Split off all GraphViz-related classes to a separate
  graphp/graphviz package.
  (#115)
• Feature: The base Graph, Vertex and EdgeBase classes can now be
  extended in order to implement a custom behavior. As such, one can now also
  instantiate them using the normal new operator instead of having to use
  Graph::createVertex() family of methods.
  (#82)
• BC break: Rename Algorithm\Directed::isDirected() to remove its ambiguity
  in regards to mixed and/or empty graphs
  (#80)

Old name	New name
Algorithm\Directed::isDirected()	Algorithm\Directed::hasDirected()

• Feature: Add new Algorithm\Directed::hasUndirected() and
  Algorithm\Directed::isMixed() in order to complement the renamed
  Algorithm\Directed::hasDirected()
  (#80)
• BC break: Walk::factoryCycleFromVertices() no longer tries to auto-complete
  a cycle if the first vertex does not match the last one, but now throws an
  InvalidArgumentException instead (#87)
• Feature: Support loop Walks, i.e. a walk with only a single edge from
  vertex A back to A (#87)
• Fix: Stricter checks for invalid cycles, such as one with an invalid
  predecessor-map or no edges at all (#87)
• Fix: The Algorithm\ShortestPath\MooreBellmanFord now also works for unweighted
  edges. This also fixes an issue where Algorithm\DetectNegativeCycle didn't work
  for unweighted edges. (#81)
• Fix: The Algorithm\MinimumCostFlow algorithms now work again. The reference
  to a non-existant class has been updated. Also fixed several issues with
  regards to special cases such as disconnected or undirected graphs.
  (#74)
• BC break: Remove unneeded alias definitions of getVertexFirst(),
  getVertexSource() and getVertexTarget()
  (#76):

Old name	New name
Graph::getVertexFirst()	Graph::getVertices()->getVertexFirst()
Walk::getVertexSource()	Walk::getVertices()->getVertexFirst()
Walk::getVertexTarget()	Walk::getVertices()->getVertexLast()