Fixed bug in posterior alpha output; added code to implement bias test from paper.
Slightly smaller sigmas in paper_test.py
Plots changed to put proxy on the x-axis.
Changed definition of alpha in posterior.py.

alpha is now defined so that

alpha = d/d(proxy) <M(proxy)>

when proxy is assumed known perfectly.
Added header line to paper_test.py
Fixed factor-of-two error in alphas of posterior.py
Tests from paper, also p-p test.  Test outputs added to .gitignore.

As written, the code will fail the p-p test for sigma_2, the small-variance
dimension.  This is due to a mismatch between the finite test prior (sigma_2
\in [0.1, 0.4]) and the (improper) analysis prior (sigma_2 > 0).  With 100
observations (default in the test), the width of the posterior in sigma_2 is
about sigma_2/10.  For sigma_2 within ~0.04 of the upper test prior boundary,
this means that the posterior will extend past the cutoff of the correct prior,
leading to bias.  But, such sigma_2 are about 10% of the total runs, leading to
failing p-p tests.  For the other variables, the posterior width is a much
smaller fraction of the prior range, so the bias is much smaller.