Gvar

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Significant performance upgrades to evalcov and evalcov_blocks,
especially for large systems.

- Fixes an inefficiency in gvar.evalcov_blocks that was introduced in v11.4.

- New optimization in gvar.evalcov for large, dense covariance matrices.
The improvement can be as large as a factor of 3-4 speedup for matrices
larger than (roughly) 200x200. Suggested by Giacomo Petrillo.

=======================
Significant rewrite of gvar.evalcov_blocks(g), making it much
faster (thanks to Giacomo Petrillo for the suggestion). Also
gvar.gvar(x,cov) has new keywords: verify and fast. See
documentation.

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Minor fixes and updates.

- Fixes (substantial) inefficiency in gvar.ode.Integrator. This was a coding
error that gave correct results but sometimes at a cost much larger than
necessary. Adds options hmax, maxstep to ode.Integrator.

- Adds gvar.abs. This is more less same as gvar.fabs, but unlike fabs works
for something like np.array([1., -2.], dtype=object). Treatment of GVars is
the same.

Versions 11.1 2020-03-01
==========================
Further upgrade to gvar.dump and gvar.load to allow
user-defined classes some control over how GVars
are removed and distributed. New functions are
available to help: gvar.remove_gvars and
gvar.distribute_gvars. These changes respond
to a feature request for the lsqfit module.

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Significant upgrade to gvar.dump and gvar.load, which now can
handle data structures that contain mixtures of GVars with
other data types, and that can include nested dictionaries, lists,
tuples, etc. The old versions (v10.1.2) of these
are still available as gvar.gdump and gvar.gload.

The new versions of dump/load are much more flexible, but
unlike the old versions only work with pickle (not json)
as the serializer; there is no longer a "method" keyword.
gdump/gload still offer a choice between pickle and json.

Other additions: gvar.dependencies, gvar.missing_dependencies,
and gvar.filter.

==========================
Fixes bug introduced into dump in version 10.1 (with thanks to
Andre Walker-Loud for pointing it out).

=========================
Fixes minor bug/inefficiency in gvar.dependencies and gvar.dump.