Lsqfit

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A minor upgrade to provide functionality for other libraries. The first
change is not backwards compatible, but is unlikely to break much or any
code (except mine).

- fit.svdcorrection is now the sum of all svdcorrections, not a vector. The
sum is all that is needed to construct error budgets, which is the
only use for fit.svdcorrection. The sum is easier to manipulate -- for
example, two svdcorrections can now be added to give a composite
svdcorrection (as opposed to concatenated before).

- Fixed innocuous bug in lsqfit.nonlinear_fit.format().

- gvar.dataset.Dataset.slice can now apply slices to multiple dimensions.

- Added __format__ to gvar.GVar. This converts the GVar to a string
and then applies the format to the string. This was needed to make
python3 and python2 function similarly in certain situations.

- More polishing of the documentation (especially about svd).

- Beginning with this version of lsqfit, version numbers will be consistent
with the rules of "semantic versioning" (http://semver.org). The most
important consequence is that any change that is *not* backwards compatible
with the current interface (as defined by the documentation) will be signaled
by a change in the major version number, where the full version number has the
format major.minor.patch (so the major version number is 5 for version 5.0).
A side effect of this is that increases in the major version number can
be triggered by relatively obscure changes in the interface that will have
no effect whatsoever on almost all existing codes. The current move to 5.0
is an example.

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This release is almost identical to the previous release. It is mainly to do
with getting the software registered properly online.

- Small improvement to the user interface in gvar.ode. It now works with
vectors of x values, returning vectors of y values.

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- Bug fix so recent changes in lsqfit don't cause crashes on Windows systems.

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Small bug fixes.

- gvar.dataset.Dataset objects now work with Python's pickle. Also
Dataset objects can now be initialized from other Dataset object, or from
dictionaries, or lists of key-data tuples (like dictionaries).

- lsqfit.wavg now works with priors.

- Removed calls to C's lgamma function because it isn't available to
old C compilers. Use Python's math.lgamma instead, which should always be
available.

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Bug fix: the new svd system didn't work with older versions of numpy (earlier
than 1.8). It now does. The problem was in lsqfit; gvar was fine.
There was a related issue in gvar.cspline which is also fixed.

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Very small additions to facilitate pickling and other serialization of GVars. Changed
gvar.evalcov and gvar.gvar so that newg = gvar.gvar(gvar.mean(g), gvar.evalcov(g))
for some array or dictionary g containing GVars creates a new array/dictionary
with the same means and covariance matrix. Added better documentation
on the gvar page about pickling gvars, and also added new functions
(dump, dumps, load, loads) for pickling collections of GVars.