Vegas

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Bug fix that allows code to work on Windows (fixes type mismatch having to do
with different conventions for integer lengths).

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vegas.PDFIntegrator rewritten to make it more efficient.
The interface is the same.

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MPI (multi-processor) support is now integrated into vegas
and automatically avaible for any integrand without modifying
its code --- simply run the code using, for example,

mpirun -np 4 python your-code.py

to distribute integrand evaluations over 4 processes (and processors if you
have that many). You no longer need to convert the integrand using
vegas.MPIintegrator; MPIintegrator is no longer needed for anything. I left it
in vegas for legacy purposes, but you should discontinue its use.

Other changes:

- The stopping conditions (atol and rtol) now work. I forgot to install
the stopping conditions in earlier versions, mostly because I never use
them. These stopping conditions can be quite unreliable in early iterations,
before vegas has converged --- use them with caution if you use them at all.
Thanks to Kevin Andrade for pointing out that they were not working.

- Given output r from a vegas integrator, added new option to r.summary().
Using r.summary(extended=True) appends a table showing the final results
for every component of the integrand (not just the part used to adapt
vegas).

- Extra documentation on how to access integrands written in C or
Fortran from Python vegas. New (simpler) documentation on using MPI.

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Added new class PDFIntegrator for evaluating expectation values weighted
by the probability density function (PDF) for arbitrary multi-dimensional
Gaussian distributions. This class once resided in module gvar but
had to be moved to vegas to avoid circular imports (which are bad) in the code.
It is part of the setup for Bayesian integrals (BayesIntegrator)
in the lsqfit module.

Also fixed a bug in MPIintegrator that caused occasional crashes.

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- Corrected small bugs in RAvg.summary(), RAvgArray.summary() and
RAvgDict.summary(). Summary tables give weighted averages when
weighted=True, unweighted averages otherwise. summary() has an
optional argument (weighted) to overwrite the default setting in
the RAvg, etc. Summary tables used to always list weighted averages,
whether or not weighted=True.

- Corrected small bug in code for batch integrands that return dictionaries.
vegas is supposed to adapt to the first entry in dictionary-valued
functions, where 'first' is defined to be the first entry in dictionary[k]
where k is the first key in dictionary.keys().

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Starting with this version, vegas requires module gvar ('pip install gvar') in
order to function. In the past it used a (very poor) substitute for gvar if
that module was not installed. That kludge is not sustainable.

- Integrand functions in the past could return numbers or numpy arrays. Now
they can also return dictionaries whose values are either numbers
or numpy arrays. This is useful in situations where multiple integrals are
being done simultaneously since the keys can be used to document and keep
straight which integral is which. This should make code easier to read and
write.

- Miscellaneous internal changes to simplify the vegas code that handles
integrands.

- Switch to pip for installing and uninstalling. It is more robust than
the alternatives.