Add Makefile for zipping reciepts to send to my accountant.

Documents/Shore/taxes/Makefile

+last_month != date +%Y-%m --date 'last month'
+last_zip != ls *.zip | sort -r | head -1
+new_files != find reciepts/ -type f -newer ${last_zip}
+
+${last_month}.zip: ${new_files}
+	zip $@ $^
+
+.PHONY: clean
+clean:
+	rm *.zip