Added Makefile and updated STL files.

Author: jcrocholl

Makefile

@@ -0,0 +1,9 @@
+all: recirculating.stl plate.stl
+
+.SECONDARY:
+
+# Explicit wildcard expansion suppresses errors when no files are found.
+include $(wildcard *.deps)
+
+%.stl: %.scad
+	openscad -m make -d $*.deps -o $@ $<