trivial bits setting rbenv version and adding a `clean` target for math replay

.rbenv-version

@@ -0,0 +1 @@
+1.9.3-p125

math-replay/Makefile

@@ -5,9 +5,18 @@ ALL += $(patsubst %.tex,%.pdf,$(shell find . -name '*.tex'))
 %.html:%.haml
 	haml -Ilib -rhaml/filters-ext $^ $@
 
+
 %.pdf:%.tex
 	texi2pdf $^ -o $@ && \
 		rm -vf $(patsubst %.pdf,%.aux,$(notdir $@)) \
 		       $(patsubst %.pdf,%.log,$(notdir $@))
 
+
 all: $(ALL)
+
+
+clean:
+	rm -vf $(ALL)
+
+
+.PHONY: all clean