Add a Makefile that uses latexmk and cleans up the .bbl files

[esba1ley]

Added Makefile for command line use to build sample-handout.pdf and sample-book.pdf.

$ make
$ make all

builds both PDF files. You can also build either one directly using the PDF file names:

$ make sample-handout.pdf
$ make sample-book.pdf

There is also a

$ make clean

which strips back to the repository contents (including PDFs). If you want to delete the PDFs, just use:

$ make clean_all