doc,tools: properly syntax highlight API ref docs

Makefile

@@ -737,7 +737,7 @@ out/doc/api/assets:
 
 # If it's not a source tarball, we need to copy assets from doc/api_assets
 out/doc/api/assets/%: doc/api_assets/% out/doc/api/assets
-	@cp $< $@
+	@cp $< $@ ; $(RM) out/doc/api/assets/README.md
 
 
 run-npm-ci = $(PWD)/$(NPM) ci

doc/api_assets/README.md

@@ -0,0 +1,27 @@
+# API Reference Document Assets
+
+## highlight.pack.js
+
+_Generated by [highlightjs.org/download][] on 2020-05-16._
+
+Grammars included in the custom bundle:
+
+* Bash
+* C
+* C++
+* CoffeeScript
+* JavaScript
+* JSON
+* Markdown
+* Plaintext
+* Shell Session
+
+## hljs.css
+
+The syntax theme for code snippets in API reference documents.
+
+## style.css
+
+The main stylesheet for API reference documents.
+
+[highlightjs.org/download]: https://highlightjs.org/download/

doc/api_assets/hljs.css

@@ -0,0 +1,23 @@
+.hljs {
+  font-weight: normal;
+  font-style: normal;
+}
+
+.hljs-symbol {
+  color: #333;
+}
+
+.hljs-keyword {
+  color: #338;
+}
+
+.hljs-string,
+.hljs-regexp,
+.hljs-number {
+  color: #E54305;
+}
+
+.hljs-comment {
+  color: #666;
+  font-weight: lighter;
+}