Improvements to the build system

Make sure the top level directory contains the resulting PDFs, but keep
the intermediate build files in a separate directory to reduce clutter.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

Makefile

@@ -1,14 +1,17 @@
 
-TEX = latexmk -recorder -pdf
+OUTPUT = build
+TEX = latexmk --output-directory=$(OUTPUT)/
+SOURCES := $(shell find -name '*.tex' | sort)
+PDFS := $(shell find -name '*.tex' | sed 's/.tex$$/.pdf/' | sort)
 
 %.pdf: %.tex
 	$(TEX) $<
 
 cheese:
-	$(TEX) -outdir=cheese/ *.tex
-	pdfjoin -o cheese.pdf cheese/*.pdf
+	$(TEX) -recorder -pdf $(SOURCES)
+	cp build/*.pdf .
+	pdfjoin -o worksheets.pdf $(PDFS)
 
 clean:
-	latexmk -C
-	rm -r cheese/
-	rm cheese.pdf
+	rm *.pdf
+	rm -r $(OUTPUT)/