refactor stat deletion code, no functional changes
delete all metrics in a folder using a command like: delcounters path.to.parent.*
delete stats via management console: move to lib/, docs, generalize, tests
Merge pull request #246 from carver/delete-group

Delete folder of metrics with: delcounters parent.path.*
Update docs to include del* commands

Updated command list to show all the delete commands, as well as adding an example to show how to delete a folder of counters.