docs: move C++ API docs to subfolder

docs/cpp-api/assets/doxygen-awesome-css/Makefile

@@ -0,0 +1,38 @@
+# SPDX-FileCopyrightText: 2022 Andrea Pappacoda <andrea@pappacoda.it>
+# SPDX-License-Identifier: MIT
+
+.POSIX:
+
+PROJECT = doxygen-awesome-css
+
+# Paths
+PREFIX = /usr/local
+DATADIR = share
+INSTALLDIR = $(DESTDIR)$(PREFIX)/$(DATADIR)/$(PROJECT)
+
+# Utilities
+INSTALL = install -m 644
+MKDIR = mkdir -p
+RM = rm -f
+
+# Files to be installed
+FILES = doxygen-awesome-darkmode-toggle.js \
+  doxygen-awesome-fragment-copy-button.js \
+  doxygen-awesome-interactive-toc.js \
+  doxygen-awesome-paragraph-link.js \
+  doxygen-awesome-sidebar-only-darkmode-toggle.css \
+  doxygen-awesome-sidebar-only.css \
+  doxygen-awesome.css
+
+# Empty targets so that `make` and `make clean` do not cause errors
+all:
+clean:
+
+install:
+	$(MKDIR) $(INSTALLDIR)
+	$(INSTALL) $(FILES) $(INSTALLDIR)/
+
+uninstall:
+	$(RM) -r $(INSTALLDIR)/
+
+.PHONY: all clean install uninstall