Added max tree depth to pslqcontext

For the most part, the mission of pslqcontext is to hold the input to the PSLQ algorithm, the known answer PSLQ is supposed to find, and the current status of the PSLQ algorithm. It contains utilities for ascertaining the status, such as the minimum and maximum norms of solution vectors.

In order to support the mission to hold the input to the PSLQ algorithm, a field for the key parameter, maxTreeDepth, was added to pslqcontext.