docs: include the logos in the generated documentation

docs/reference/api/Makefile.am

@@ -13,6 +13,12 @@ DIAGRAMS_PNG = $(notdir $(DIAGRAMS:.dia=.png))
 $(DIAGRAMS_PNG): $(DIAGRAMS)
 	$(AM_V_GEN) $(DIA) -t png $^ 1>/dev/null 2>&1
 
+# Logos
+LOGOS_PNG = \
+	$(top_srcdir)/data/ModemManager-logo-square.png \
+	$(top_srcdir)/data/ModemManager-logo-wide.png \
+	$(top_srcdir)/data/ModemManager-logo-wide-text.png
+
 # The name of the module.
 DOC_MODULE = ModemManager
 
@@ -53,6 +59,7 @@ MKDB_OPTIONS = --output-format=xml --sgml-mode --name-space=mm
 # Images to copy into HTML directory
 HTML_IMAGES = \
 	$(DIAGRAMS_PNG) \
+	$(LOGOS_PNG) \
 	$(NULL)
 
 #  Note that PNG files are also added in content_files so that
@@ -114,6 +121,9 @@ CLEANFILES += \
 	-rf xml html tmpl \
 	$(NULL)
 
-# PNGs generated are removed only in maintainer-clean
-MAINTAINERCLEANFILES = \
-	$(DIAGRAMS_PNG)
+# PNGs are removed only in dist-clean
+# Diagrams are generated by dia in the current directory
+# Logos are copied to current directory by gtk-doc
+DISTCLEANFILES = \
+	$(DIAGRAMS_PNG) \
+	$(notdir $(LOGOS_PNG))

docs/reference/api/ModemManager-docs.xml

@@ -6,7 +6,16 @@
 <book id="ModemManager" xmlns:xi="http://www.w3.org/2003/XInclude">
   <bookinfo>
     <title>ModemManager Reference Manual</title>
-    <releaseinfo>For ModemManager version &version;</releaseinfo>
+    <subtitle>
+      <inlinemediaobject>
+        <imageobject>
+          <imagedata fileref="ModemManager-logo-wide.png" format="PNG" align="center"/>
+        </imageobject>
+      </inlinemediaobject>
+    </subtitle>
+    <releaseinfo>
+      For ModemManager version &version;
+    </releaseinfo>
 
     <authorgroup>
       <author>