refactor: rely on Jekyll to number sections

-   One less build step, one less Python script

CONTRIBUTING.md

@@ -21,6 +21,14 @@ All contributors will be acknowledged.
  If you add a new example,
  please add a corresponding rule in `Makefile`.
 
+- Use `{% raw %}{% include h2_numbered.md title="words" %}{% endraw %}`
+ to create a numbered section
+ that includes a runnable code example.
+
+- Use `{% raw %}{% include h2_unnumbered.md title="words" %}{% endraw %}`
+ to create an unnumbered section
+ that *doesn't* include a runnable code example.
+
 - Use `{% raw %}{% include double.md stem="file" suffix="sql out" %}{% endraw %}`
  in `index.md` to include `src/file.sql` and `out/file.out`.
  (Any two suffixes can be provided, such as `"py out"`.)
@@ -43,6 +51,9 @@ All contributors will be acknowledged.
  solid 1-point black lines,
  and unfilled objects.
 
+- All external links are written using `{% raw %}[box][notation]{% endraw %}` inline
+ and defined at the foot of the document.
+
 ## Logical Structure
 
 - Introduction
@@ -64,9 +75,6 @@ All contributors will be acknowledged.
 - Appendices
  - A *glossary* that defines terms called out in the episodes.
  - *Acknowledgments* that point at inspirations and thank contributors.
-- Links
- - All external links are written using `{% raw %}[box][notation]{% endraw %}` inline
- and defined at the foot of the document.
 
 ## Physical Structure
 

Makefile

@@ -77,11 +77,6 @@ used:
 freq:
  @python bin/get_sql_features.py --report freq --files ${SQL_FILES}
 
-## renumber: renumber headings
-.PHONY: renumber
-renumber:
- @python bin/renumber_headings.py ${PAGE}
-
 ## run: re-run all examples
 .PHONY: run
 run: ${OUT_FILES}

_includes/h2_numbered.md

@@ -0,0 +1 @@
+## {% increment h2_counter %}: {{include.title}}

_includes/h2_unnumbered.md

@@ -0,0 +1 @@
+## ☆ {{include.title}}

_includes/init_counters.md

@@ -0,0 +1,6 @@
+{%- comment -%}
+Initialize per-file counters.
+- Needed so that first use yields 1 instead of 0.
+- Must be included in the source file to ensure correct initialization order.
+{%- endcomment %}
+<!-- {% increment h2_counter %} -->