- move TargetInfo and RunInfo docs into the new output API doc
- remove the old developer_reference/APIs.rst as obsolete
- Update output API tag reference to point to the new doc
- Add a reference tag for metadata
- Remove doc/source/api from .gitignore -- this is no longer
auto-generated.
- Add a top-level "index" for the API documentation.
- Add output API documentation.
- Remove the output API example file, as its contents is now part of the
output API docs.
