New example_synth code

`example_synth.rst` updated down to coarse-grain representation.

docs/source/code_examples/example_synth/Makefile

@@ -0,0 +1,15 @@
+PROGRAM_PREFIX :=
+
+YOSYS ?= ../../../../$(PROGRAM_PREFIX)yosys
+
+DOTS = control_hier.dot control_proc.dot
+DOTS += example_hier.dot
+
+dots: $(DOTS) example.out
+
+$(DOTS) example.out: example.v example.ys
+	$(YOSYS) example.ys -l example.out -Q
+
+.PHONY: clean
+clean:
+	rm -f *.dot