Analytic tests

The analytic formulas exist, as much as possible, and are used in plot.densities and plot.moments, which are the new names for the correctness tests after I gutted and fixed everything I did wrong the first time I designed it.
The problems left are that the t-distribution part is buggy **and** I haven't dug up the analytic t-variance (which I don't want to do until I figure out what the bug is). I probably just typed the parameters in wrong (in NIW.marginals), or maybe the dt.density function is broken. I dunno because I haven't actually run it indepently of the whole framework. Can you take a look? I'm sick of it at this point and tempted to just comment it out the window and stick with the computational method--at least that method gave us lines for everything!!

What a jerk this was.

I'm going to sleep for 4 hours, then give you a ring, eh? We need to write the report quickfast, and finish the Rdocs. I'm going to prioritize that when I wake up. If there's time left over, I want to tweak rNIW so that it doesn't duplicate rMNIW, and get the sourceCpp call to the top of the file.