Replace Set in graphlib with Set from cp-set
Do not include graph string representation in error messages
s/"/'/ for test code
Remove data.Set and data.PriorityQueue
Improve test coverage for BaseGraph
Prev v0.6.0 release
Bump version and set as pre-release
Use cp-data v1.1.0
Change uses of cp-set to cp-data
Merge branch 'master' of https://github.com/cpettitt/graphlib