doc/Doxyfile.in: adjust paths to top_builddir

If we work out of tree some files are build in top_builddir and not in
top_souredir.
Also fix up the used libcoap API versin by using a global variable here.

doc/Doxyfile.in

@@ -756,7 +756,7 @@ WARN_LOGFILE           =
 INPUT                  = @top_srcdir@/doc/main.md \
                          @top_srcdir@/src \
                          @top_srcdir@/include/coap@LIBCOAP_API_VERSION@ \
-                         @top_srcdir@/doc/man_tmp
+                         @top_builddir@/doc/man_tmp
 
 # 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
@@ -792,7 +792,7 @@ RECURSIVE              = NO
 # run.
 
 EXCLUDE                = @top_srcdir@/src/coap_io_lwip.c \
-                         @top_srcdir@/include/coap2/lwippools.h
+                         @top_srcdir@/include/coap@LIBCOAP_API_VERSION@/lwippools.h
 
 # The EXCLUDE_SYMLINKS tag can be used to select whether or not files or
 # directories that are symbolic links (a Unix file system feature) are excluded
@@ -825,7 +825,7 @@ EXCLUDE_SYMBOLS        =
 # that contain example code fragments that are included (see the \include
 # command).
 
-EXAMPLE_PATH           = @top_srcdir@/doc/man_html
+EXAMPLE_PATH           = @top_builddir@/doc/man_html
 
 # If the value of the EXAMPLE_PATH tag contains directories, you can use the
 # EXAMPLE_PATTERNS tag to specify one or more wildcard pattern (like *.cpp and