fix variant path for footer generated file

Tuprules.tup

@@ -1,16 +1,17 @@
 &root = .
-&build_root = build
+&tmpl_dir = ./templates
+&gen_tmpl_dir = ./build/templates
 
 HTML_TEMPLATE = main.html
 
-!html = | &(root)/templates/footer.html \
+!html = | &(tmpl_dir)/<tmpl_group> \
 	|> ^b html %f^ \
 	pandoc --from markdown --to html \
-	--template=&(root)/templates/$(HTML_TEMPLATE) \
+	--template=&(tmpl_dir)/$(HTML_TEMPLATE) \
+	--include-in-header=&(tmpl_dir)/header.html \
+	--include-before-body=&(tmpl_dir)/nav.html \
 	--css &(root)/css/style.css \
-	--include-in-header=&(root)/templates/header.html \
-	--include-before-body=&(root)/templates/nav.html \
-	--include-after-body=&(build_root)/templates/footer.html \
+	--include-after-body=&(gen_tmpl_dir)/footer.html \
 	%f | sed 's|%%webRoot%%|&(root)|g' > %o \
 	|> %B.html
 

templates/Tupfile

@@ -1 +1 @@
-: |> ./generate_footer.sh > %o |> footer.html
+: |> ./generate_footer.sh > %o |> footer.html ./<tmpl_group>