Allow 'add node' and 'add edge' to add more than one
Trace path from start to finish in critical path example
Automatically numericize numerical node names

This means we do not need to do hacks like (1+0) due to type issues,
since all number-like node names are now converted to numbers.
Fix strings prefixed by numbers being compared as numbers
Add BFS example
Merge pull request #32 from Muon/master

Critical path trace, BFS example, adding multiple nodes, bugfix