Jackson 3 series companion code

37 runnable examples covering the eight feature posts on ankurm.com, verified
against Jackson 3.2.1 on Temurin 21.0.5. Every output committed under docs/ was
produced by run-all.sh.

Also documents 11 places where the published snippets do not compile or do not
behave as printed against a real Jackson 3 build - most notably that
writeValueAsString(List<Base>) silently drops the polymorphic type discriminator,
so the post's serialised output cannot be read back.

docs/README.md

@@ -0,0 +1,18 @@
+# Documentation
+
+One page per post in the series. Each page lists the examples for that post, states
+where the code deviates from the published snippet and why, and embeds the real
+captured output.
+
+- [Part 0 — Jackson 101: setup and the ObjectMapper lifecycle](part0-setup.md)
+- [Part 1 — ObjectMapper: reading and writing](part1-objectmapper.md)
+- [Part 2 — Records, Optionals and sealed types](part2-modern-java.md)
+- [Part 3 — Annotations](part3-annotations.md)
+- [Part 4 — Custom serialisers, deserialisers and mix-ins](part4-custom.md)
+- [Part 5 — Polymorphic deserialisation](part5-polymorphic.md)
+- [Part 6 — Streaming API and the tree model](part6-streaming.md)
+- [Part 7 — Security](part7-security.md)
+- [Beyond the posts](beyond.md)
+
+Raw captured stdout for every program is in [`output/`](output). Those files are
+regenerated by [`../run-all.sh`](../run-all.sh); do not edit them by hand.