Added generic timer utility

make-timer creates a structure that records the elapsed time of a given expression
by use of the macro, time-this, which consumes a timer and an expression, starts the timer,
evaluates the expression, stops the timer, and finally returns the value that was returned by the expression.
added some timing calls for phase1 and phase2
Merge branch 'lexishift' of https://github.com/wfi/puzzle-solver into lexishift
Resolving conflicts in timing data collection and frequency distribution collection

Conflicts:
	stp-solve-cluster.rkt
Merge branch 'lexishift' of https://github.com/wfi/puzzle-solver into lexishift
cleanup from most recent merge