MCMC WCS tweak test, library

My very simple, very slow, very limited WCS tweak code based on MCMC (see two days ago) is tested and works. A code that iteratively linearizes the WCS derivatives around the iteratively updated tangent plane projection will be much faster, but takes more thought to do correctly. The MCMC code can be used, I guess, to check the output of the linearized code once I write the latter.

My friend Darcy Duke helped me find papers (on the "lost in space" problem) in the MIT Engineering Library.