toh: Parse -d and -q command line options

This adds the ability to set the number of disks by passing the -d flag
at execution, and adds an option to run quietly.
toh: s/_INPUT/_BACKEND/g
toh: Define eprintf()

This adds a convience macro for print message to stderr.
toh: Add IS_LEGAL_MOVE() macro
toh: Add game function prototypes
toh: Define mprintf() macro

Replace inline message function with a macro which rids the need for the
user of vprintf.
toh: Set backend with makefile variable

It is no longer necessary to manually -D define the backend variable at
compile time, instead, set the BACKEND variable when invoking make.