doc: use doxygen-awesome theme

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "contrib/doxygen-awesome-css"]
+	path = contrib/doxygen-awesome-css
+	url = https://github.com/jothepro/doxygen-awesome-css.git

CMakeLists.txt

@@ -12,6 +12,17 @@ endif()
 
 find_package(Git QUIET)
 if(GIT_FOUND AND EXISTS "${PROJECT_SOURCE_DIR}/.git")
+    option(GIT_SUBMODULE "Update git submodules during build" ON)
+    if(GIT_SUBMODULE)
+        message(STATUS "Git submodule update")
+        execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive
+                        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+                        RESULT_VARIABLE GIT_SUBMOD_RESULT)
+        if(NOT GIT_SUBMOD_RESULT EQUAL "0")
+            message(FATAL_ERROR "git submodule update --init --recursive failed with ${GIT_SUBMOD_RESULT}, please checkout submodules")
+        endif()
+    endif()
+
     execute_process(
         COMMAND ${GIT_EXECUTABLE} rev-parse --short HEAD
         WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"

doc/Doxyfile.in

@@ -1245,7 +1245,7 @@ HTML_STYLESHEET        =
 # list). For an example see the documentation.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_EXTRA_STYLESHEET  =
+HTML_EXTRA_STYLESHEET  = @CMAKE_CURRENT_SOURCE_DIR@/doxygen-awesome.css
 
 # The HTML_EXTRA_FILES tag can be used to specify one or more extra images or
 # other source files which should be copied to the HTML output directory. Note

doc/doxygen-awesome.css

@@ -0,0 +1 @@
+../contrib/doxygen-awesome-css/doxygen-awesome.css