Some changes to the usage info for StructAlign.
Added a combination move for sigma and epsilon, and changed the starting
value of epsilon, in order to alleviate issues whereby different
proposal weights and proposal distribution type could end up giving
different answers (presumably because sigma was being allowed to get
very close to zero while epsilon was still large, and then by the time
epsilon had come back down to a reasonable value, the burnin would have
been over, such that the proposal variance for sigma would be too small
in order to allow it to jump away from zero -- a smaller starting
value for epsilon, and joint proposals for epsilon and sigma seems to
alleviate this problem).