v4.1 (#11)

- Add `Json` module to return JSON strings and write JSON as it's read to a `PipeWriter`
- Add `docfx`-based documentation to allow how-to docs and API docs to be generated on the same site

Reviewed-on: #11

docs/advanced/index.md

@@ -0,0 +1,16 @@
+# Advanced Usage
+
+_<small>Documentation pages for `BitBadger.Npgsql.Documents` redirect here. This library replaced it as of v3; see project home if this applies to you.</small>_
+
+While the functions provided by the library cover lots of use cases, there are other times when applications need something else. Below are some of those.
+
+- [Customizing Serialization][ser]
+- [Related Documents and Custom Queries][rel]
+- [Transactions][txn]
+- [Referential Integrity with Documents][ref] (PostgreSQL only; conceptual)
+
+
+[ser]: ./custom-serialization.md "Advanced Usage: Custom Serialization • BitBadger.Documents"
+[rel]: ./related.md "Advanced Usage: Related Documents • BitBadger.Documents"
+[txn]: ./transactions.md "Advanced Usage: Transactions • BitBadger.Documents"
+[ref]: /concepts/referential-integrity.html "Appendix: Referential Integrity with Documents &bull; Concepts &bull; Relationanl Documents"