gplepage/lsqfit: lsqfit version 9.0

This version offers a major overhaul of the underlying fitting strategies used by lsqfit, featuring more modern alternatives that can be more robust and/or much faster than before. See the Faster Fitters section of the tutorial in the documentation for details. Large parts of the documentation have been rewritten, especially in the tutorial which has more and simpler examples. New options exist for fitting very large uncorrelated data sets. This is the first version of lsqfit that can be created without Gnu's GSL library (provided scipy is installed), although building with GSL is still recommended.