do not hardcode version in doxyfile.in, subst it from waf instead

doxyfile.in

@@ -31,7 +31,7 @@ PROJECT_NAME           = "Jack2"
 # This could be handy for archiving the generated documentation or
 # if some version control system is used.
 
-PROJECT_NUMBER         = 1.9.11
+PROJECT_NUMBER         = @VERSION@
 
 # The OUTPUT_DIRECTORY tag is used to specify the (relative or absolute)
 # base path where the generated documentation will be put.

wscript

@@ -743,7 +743,8 @@ def build(bld):
             source = 'doxyfile.in',
             target = 'doxyfile',
             HTML_BUILD_DIR = html_build_dir,
-            SRCDIR = bld.srcnode.abspath()
+            SRCDIR = bld.srcnode.abspath(),
+            VERSION = VERSION
         )
 
         # There are two reasons for logging to doxygen.log and using it as