add initial version of pandoc filter

Makefile

@@ -12,20 +12,30 @@ OUTPUTSTYLE = $(patsubst %,$(BUILDDIR)/%,$(STYLE))
 
 OUTPUT = $(OUTPUTPAGES) $(OUTPUTSTYLE)
 
+LANGFILTER = $(TMPDIR)/langfilter
+EXECS = $(LANGFILTER)
+
 .PHONY: all
 all: build
 
 .PHONY: build
 build: $(OUTPUT)
 
-$(BUILDDIR)/%.html: $(PAGESDIR)/%.md $(TEMPLATE)
+$(BUILDDIR)/%.html: $(PAGESDIR)/%.md $(TEMPLATE) $(LANGFILTER)
 	mkdir -p $(dir $@)
-	pandoc -s --toc --template $(TEMPLATE) -o $@ $<
+	pandoc -s --toc --template $(TEMPLATE) --filter $(LANGFILTER) -o $@ $<
 
 $(BUILDDIR)/%: %
 	mkdir -p $(dir $@)
 	cp $< $@
 
+$(LANGFILTER): langfilter/*.hs langfilter/langfilter.cabal
+	mkdir -p $(dir $@)
+	cabal build -v0 all
+	find dist-newstyle -name $(notdir $@) \
+	  -print -type f -exec cp {} $(TMPDIR) \;
+
+
 .PHONY: clean distclean
 clean:
 	rm -rf $(BUILDDIR)