Implemented localEpsilon mode, whereby B-factor information provided as
an optional fourth column in the .coor file is used to weight the
contribution of epsilon on a per-site basis. This helps account for
differential flexibility and uncertainty at different regions of the
structure. The cost is an increase in runtime of ~2 fold, since the
covariance matrix is now different for each column, and the Cholesky
decompositions cannot be cached.