Gvar

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- Further fixes to gvar.dataset.avg_data(dataset). The previous
fix (in v11.8) could lead to problems for dictionary datasets
where entries dataset[k] have different sample sizes. The new
version has a new keyword (mismatch) that offers three options
for dealing with this situation.

- Several functions (eg, gvar.var) generated segmentation errors if GVars
in the arguments were replaced by None. This has been fixed. What happens
in such cases depends on the function, but segmentation faults should
not happen.

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Small upgrade to support feature request: dataset.avg_data(dataset) no longer
discards data when dataset is a dictionary whose entries have different
sample sizes. It used to truncate entries that had more samples (by
discarding from the end) so that all entries had the same (smallest)
sample size.

Also added keyword uniform to raniter.

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- Adds support for multivariate power series to gvar.powerseries, as well
as minor bug fixes. Adds error function (erf(powerseries)).

- Adds new numerical analysis module for Pade approximants of functions.

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- gvar.regulate is a new tool for regulating singularities
in correlation matrices. It has two regulation schemes,
one tailored for Cholesky decompositions of the
correlation matrix (eps), and the other using an
SVD decomposition (svdcut). The Cholesky/eps scheme is
typically a bit faster, but is less robust numerically.
The SVD scheme uses gvar.svd. The Cholesky implementation
is based on a recommendation from Giacomo Petrillo.

- Keyword add_svdnoise in gvar.svd has been replaced by keyword noise.
The old keyword still works, however (for legacy code).

- gvar.chi2, gvar.raniter, gvar.bootstrap_iter now have the option
of specifying either eps or svdcut (passed on to gvar.regulate).

- More efficient implementations of gvar.sdev and gvar.var.

==========================
Fix documentation problems introduced in 11.5.1.

==========================
More tuning of evalcov, for better performance on dense matrices of
size 15x15 or larger. Also improved doc-strings for Cython-generated
functions.