Gvar

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Significant improvement to gvar.dump/load and some new functions.
All changes are backwards compatible. Note that this code
still works with Python 2.7 (as well as Python 3.X, of course)
but it seems likely this will not continue far into
the future, as developers for the several packages
used by gvar abandon Python2, now that it is formally
discontinued.

- New versions of gvar.dump and gvar.dumps that can preserve
dependencies between derived and primary GVars (to allow, for
example, the construction of error budgets). Update for
pickling of gvar.BufferDicts.

- New function gvar.qqplot() for making QQ-plots.

- Slight modification of gvar.chi2() to support
implementation of gvar.qqplot().

- New function gvar.is_primary(g) to determine whether GVars
are primary or derived. Also gvar.GVar.is_primary(). Also
new function gvar.dependencies for collecting relevant
primary GVars.

- Function gvar.deriv(g, x) now works for an array x of GVars
(not just a single GVar). Also gvar.GVar.deriv(x).

- Fixed bug (that caused crashes) in (undocumented) low-level
gvar.gvar() usage.

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Changed default string representation used when
printing GVars so that it always shows all
significant digits in the mean. This was
not the case before when answers were
very accurate.

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Bug fix so that gvar.cspline.CSpline works with only 2 knots.

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Bug fix for Windows users (thanks to Christoph Gohlke).

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New features and improvements to existing features.
There are incompatible changes in gvar.loads and
gvar.cspline.CSpline, though most old code should
still run.

- gvar.cspline.CSpline has been reimplemented. It now supports
different algorithms (select using keyword alg) and the
default algorithm is a monotonic spline rather than a
classical cubic spline.

- Adds support in gvar.BufferDict for uniform distributions: see
gvar.BufferDict.uniform. This is for use by lsqfit.

- gvar.load() and gvar.dump() use a new protocol (for serializing
GVars) that make them substantially more efficient for large
problems. gvar.load() can read files created with the
old protocol, but if you want to update the format used
in an old file, load it and dump it again:
dump(load('filename'), 'filename'). gv.loads() no longer
has a method keyword since the method is inferred from
the data.

- Pickle format used for BufferDicts is changed but the new code
can handle data from pervious versions.

- New option (compress) for gvar.evalcov_blocks().

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- Fixes bugs in gvar.load and gvar.dump caused by recent security upgrades
to pyYAML.