Update doxygen build

docs/Makefile

@@ -2,6 +2,8 @@
 #
 SPHINX_BUILD_DIR = build
 DOXYGEN_INDEX = $(SPHINX_BUILD_DIR)/doxygen/html/index.html
+EXTRA_STYLESHEET_URL = https://github.com/jothepro/doxygen-awesome-css.git
+DX_HTML_EXTRA_STYLESHEET  = doxygen-awesome-css/doxygen-awesome.css
 
 # rules
 #
@@ -10,19 +12,22 @@ all: doxygen sphinx
 .PHONY: sphinx doxygen
 
 doxygen: $(DOXYGEN_INDEX)
-$(DOXYGEN_INDEX):
+$(DX_HTML_EXTRA_STYLESHEET):
+	git clone $(EXTRA_STYLESHEET_URL)
+
+$(DOXYGEN_INDEX): Doxyfile $(DX_HTML_EXTRA_STYLESHEET)
 	mkdir -p $(@D)
-	doxygen Doxyfile
+	doxygen $<
 
 $(SPHINX_BUILD_DIR)/index.html: index.rst atrip.rst conf.py
 	sphinx-build . $(SPHINX_BUILD_DIR)
 sphinx: $(SPHINX_BUILD_DIR)/index.html
 
 index.rst: ../README.rst
-	mv $< $@
+	cp $< $@
 
 atrip.rst: ../atrip.rst
-	mv $< $@
+	cp $< $@
 
 ../%.rst:
 	make -C $(dir $@) $(notdir $@)