docs(example): add overview template
chore(package.json): use graceful-fs and rimraf

This gets around various file related errors when loading lots of files.
fix(gen-docs): use rimraf to delete the output folder reliably
fix(doc-extractor): handle multiple paths correctly
feat(doc-extractors): store base-path in case needed later
docs(example): specify content folders explicitly

Otherwise they get put in the content folder under the build folder.