Make doxyfile out-of-tree capable

Doxyfile.in

@@ -45,7 +45,7 @@ PROJECT_BRIEF          =
 # exceed 55 pixels and the maximum width should not exceed 200 pixels.
 # Doxygen will copy the logo to the output directory.
 
-PROJECT_LOGO           = doxygen-layout/images/igh+logo.svg
+PROJECT_LOGO           = @top_srcdir@/doxygen-layout/images/igh+logo.svg
 
 # The OUTPUT_DIRECTORY tag is used to specify the (relative or absolute)
 # base path where the generated documentation will be put.
@@ -655,9 +655,9 @@ WARN_LOGFILE           =
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  = master \
-                         include \
-                         devices/ecdev.h
+INPUT                  = @top_srcdir@/master \
+                         @top_srcdir@/include \
+                         @top_srcdir@/devices/ecdev.h
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is
@@ -886,13 +886,13 @@ HTML_FILE_EXTENSION    = .html
 # have to redo this when upgrading to a newer version of doxygen or when
 # changing the value of configuration settings such as GENERATE_TREEVIEW!
 
-HTML_HEADER            = doxygen-layout/style/html_header.html
+HTML_HEADER            = @top_srcdir@/doxygen-layout/style/html_header.html
 
 # The HTML_FOOTER tag can be used to specify a personal HTML footer for
 # each generated HTML page. If it is left blank doxygen will generate a
 # standard footer.
 
-HTML_FOOTER            = doxygen-layout/style/html_footer.html
+HTML_FOOTER            = @top_srcdir@/doxygen-layout/style/html_footer.html
 
 # The HTML_STYLESHEET tag can be used to specify a user-defined cascading
 # style sheet that is used by each HTML page. It can be used to
@@ -903,8 +903,8 @@ HTML_FOOTER            = doxygen-layout/style/html_footer.html
 
 HTML_STYLESHEET        =
 
-HTML_EXTRA_STYLESHEET  =  doxygen-layout/style/custom.css \
-                          doxygen-layout/style/custom_igh_theme.css
+HTML_EXTRA_STYLESHEET  =  @top_srcdir@/doxygen-layout/style/custom.css \
+                          @top_srcdir@/doxygen-layout/style/custom_igh_theme.css
 
 
 # The HTML_EXTRA_FILES tag can be used to specify one or more extra images or