Minor.
More work on posts_indexer/metadata_aggregator, kinda works, needs refactoring.
Support relative and absolute paths in includes_transformer.
Updates in pubspec, docs.
* Removed special cases from MetadataAggregator.
* IncludeTransformer -> PartialTransformer.
* Cleanup, improved docs.
No rewriting of post paths, simplifies code.
Minor.