Lsqfit

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Two minor bug fixes in MultiFitter.

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New implementation of lsqfit.MultiFitter that offers new features but also
is (slightly) incompatible with previous versions. The most important
new feature is the ability to change fitter keyword values in the middle
of fit chain, by including a dictionary with the new values as
an entry in the models list. This allows far more control over the
individual fits in chain of fits.

The incompatibilities mostly affect chained fits and are mostly internal. The
list of chained fits (fit.chained_fit) now contains all fits, including the
wavg fits done after a parallel fit. The output from fit.formatall() differs
accordingly. Another change for all fits: bootstraps are initiated using the
fit (not the fitter, as before) -- eg, fit.bootstrapped_fit_iter(10).

Other changes:

- maxit=0 normally results in one iteration of the nonlinear_fit fitter.
As per a request from Jason Chang, this is no longer the case when linear
terms are specified (using the linear keyword). Then the prior is used for
the nonlinear terms, and the linear terms are determined using the linear
least-squares formula (variable projection). This is an efficient way to
determine linear parameters when you have good estimates (eg, from previous
fits in a chain) for the nonlinear parameters.

- Use of a prior in lsqfit.wavg is deprecated. A prior never made much sense.

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- lsqfit.nonlinear_fit has a new keyword: linear. This can be used
to specify a list of fit variables that appear linearly in the fit
function. These are removed from the fit using variable projection, thereby
reducing the number of fit parameters; they are reintroduced after the fit.
This parameter is optional and currently somewhat experimental.

- nonlinear_fit methods load_parameters and dump_p are deprecated; use
gvar.load and gvar.dump instead. Similarly dump_pmean is
deprecated.

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- p0=True generates a random p0 from the prior in nonlinear_fit. This
can be useful for fits that are sensitive to the starting point.

- Updated time measurements for Python3.

- Improved makefile and pypi documentation.

- Fixed issue in tests.

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- Adds bootstrapped_fit_iter to MultiFitter (analogous to same for
nonlinear_fit).

- Minor bug fixes in nonlinear_fit.bootstrapped_fit_iter.

- Method name bootstrap_iter replaced by bootstrapped_fit_iter, but old
name still present, for legacy code.

- Improved setup.py.

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Minor update.

- MultiFitter.make_plot now has a choice of views (ratio, diff, log, ...).

- Minor fix in examples/nist.py to deal with changes in numpy.