Switching example synth to fifo

Fifo code based on SBY quick start.
Instead of showing the full design we are (currently) focusing on a single output (rdata), using `%ci*` to get the subcircuit it relies on.

docs/source/code_examples/fifo/Makefile

@@ -0,0 +1,16 @@
+PROGRAM_PREFIX :=
+
+YOSYS ?= ../../../../$(PROGRAM_PREFIX)yosys
+
+DOTS = addr_gen_hier.dot addr_gen_proc.dot
+DOTS += rdata_proc.dot rdata_flat.dot
+DOTS += fifo_flat.dot fifo_synth.dot
+
+dots: $(DOTS) fifo.out
+
+$(DOTS) fifo.out: fifo.v fifo.ys
+	$(YOSYS) fifo.ys -l fifo.out -Q
+
+.PHONY: clean
+clean:
+	rm -f *.dot