Change HDF5 output slightly.

* Move stuff that affineEnsemble outputs to HDF5 into subgroups:
   AffineSettings for stuff about the mcmc params, ParamInfo for
   stuff about the actual parameters, Chains for the actual chains.
* Fixed some places where H5Sclose wasn't being called.
Add methods to return class, method, string from error.

*Useful for contructing new errors out of old ones.