improvements to computeH_PYM

Adding warning for nan or inf-valued hessians. Adding the option of
returning the empirical Bayes estimate of entropy (rather than
performing the full 2d integral over alpha and d). Addressing potential
numerical problems arising from normalizing the log likelihood using
its value at the MAP.
minor changes to the summary text

fixing a typo or two.
test_HPYM_randomized now generates new test values to current directory