docs: include doxygen-awesome theme

.gitmodules

@@ -14,3 +14,6 @@
 [submodule "src/ifcconvert/cityjson"]
 	path = src/ifcconvert/cityjson
 	url = https://github.com/IfcOpenShell/ifc-to-cityjson
+[submodule "docs/assets/doxygen-awesome-css"]
+	path = docs/assets/doxygen-awesome-css
+	url = https://github.com/jothepro/doxygen-awesome-css.git

docs/Doxyfile

@@ -944,9 +944,9 @@ WARN_LOGFILE           =
 # Note: If this tag is empty the current directory is searched.
 
 INPUT                  = ../src/ifcgeom \
-                         ../src/serializers \
                          ../src/ifcgeom_schema_agnostic \
-                         ../src/ifcparse
+                         ../src/ifcparse \
+                         ../src/serializers \
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses
@@ -1311,7 +1311,7 @@ HTML_STYLESHEET        =
 # documentation.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_EXTRA_STYLESHEET  =
+HTML_EXTRA_STYLESHEET  = assets/doxygen-awesome-css/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
@@ -1334,7 +1334,7 @@ HTML_EXTRA_FILES       =
 # The default value is: AUTO_LIGHT.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_COLORSTYLE        = AUTO_LIGHT
+HTML_COLORSTYLE        = LIGHT # required by doxygen-awesome with Doxygen >= 1.9.5
 
 # The HTML_COLORSTYLE_HUE tag controls the color of the HTML output. Doxygen
 # will adjust the colors in the style sheet and background images according to
@@ -2166,7 +2166,7 @@ MAN_LINKS              = NO
 # captures the structure of the code including all documentation.
 # The default value is: NO.
 
-GENERATE_XML           = YES
+GENERATE_XML           = NO
 
 # The XML_OUTPUT tag is used to specify where the XML pages will be put. If a
 # relative path is entered the value of OUTPUT_DIRECTORY will be put in front of