Add alchemist from Perceptive CodeDash 2014

This is a simple undirected, unweighted shortest path problem, but
clothing it as transmuting elements was pretty clever--nicely done,
@PerceptiveSoftwareCodeDash! The brute-force solution here is OK here
due to small graph size and laziness of solution generation, but
something smarter would be nice.

I wonder if this might be a good, small-enough problem on which to
finally write some transducers code instead of just reading about it...