Remove requirement for existing edges
Remove unneeded code (duplicate of base class)
Properly throw UnexpectedValueException for unconnected graphs
Consider null weight to be zero instead of bailing out
Improve documentation
Move duplicate logic to base class
Additional helper `getWeight()`
Add support for directed and mixed graphs
Add proper unit tests for minimum spanning tree (~95% coverage)
Merge branch 'master' into improve-minimumspanningtree
Add improved minimum spanning tree to CHANGELOG
Improve test case for 100% coverage
Merge pull request #73 from clue/improve-minimumspanningtree

Improve Algorithm\MinimumSpanningTree