Optimized Problem 14 so that it recursively solves the chains

Much better! Down to about 4 seconds to solve. Used 3 times the ceiling to
store the found chains since that should be reasonable. Also, the recursive
nature allows me to fill the chain as I go.
Solved Problem 15: http://projecteuler.net/problem=15

Answer: 137846528820

A combination problem.
Solved Problem 92: http://projecteuler.net/problem=92

Answer: 8581146

The running time is still about a minute which means I should be able to cut it
down a bit more.