ExampleGroup: "root example group" not in name

Fixes #168. Like, for realsies this time (unlike #169).

Also fix access control and add documentation to a variety of Example
and ExampleGroup classes and methods.
ExampleGroup: fix access control, add docblocks

ExampleGroup methods were undocumented, and did not have any access
modifiers specified. Add documentation and more granular access control.
Merge pull request #187 from modocache/168-fix-root-example-groups

ExampleGroup: "root example group" not in name