Add Tree algorithms (skeleton)
Add unit tests for directed trees (100% coverage)
Add depth-first search for checking tree
Properly stop recursion and only check in isTree()
Throw Exceptions for parallel edges
Tests for parallel/loop/undirected edges (100% coverage)
Move Set::hasFlow() to new Algorithm\Flow
Add tests with 100% coverage for Algorithm\Flow
Improve tree documentation
Remove Vertex::isLeaf() (see Algorithm\Tree\Undirected::isVertexLeaf())
Add Algorithm\Tree to CHANGELOG
Implement Algorithm\Tree\Undirected + 100% code coverage
Improve documentation
Add new Algorithm\Flow to CHANGELOG
Move Vertex::getFlow() to Algorithm\Flow::getFlowVertex()
Document moved Vertex::getFlow()
Merge Algorithm\Balance into Algorithm\Flow
Document Algorithm\Balance in now part of Algorithm\Flow
Fix missing import
Add tests with 100% code coverage for Algorithm\Flow