Vegas

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Very minor fix: changes in numpy v1.9 broke MPIintegrand. It is now
fixed.

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This is a minor bug fix release.

- Fixed a bug that caused option adapt_to_errors to malfunction. The
malfunction caused the integral to be less than optimal, although
still correct.

- Cleaner implementation of the (Feynman) path integral example.

=========================
There is a new decorator, vegas.MPIintegrand, that makes it trivial to
evaluate integrands on mupliple processors using MPI. See the tutorial section
on Multiple Processors for more discussion. This is only useful for
integrands that are expensive to evaluate.

Beginning with this version of vegas, 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 2 for version 2.1.4).
A side effect of this policy is that increases in the major version number can be
triggered by relatively obscure changes in the interface that have no
effect whatsoever on almost all existing codes. The minor component increased
for this version because it adds new functionality; but it remains compatible
with the previous version.

============================
More small changes (all backwards compatible).

- vegas.Integrator has new parameter ran_array_generator. This is the random
number generator used by vegas. The default function is numpy.random.random.
The new parameter allows users to substitute a different random number
generator, if they wish.

- Legacy name vegas.VecIntegrand now works. This isn't needed for new code
(use vegas.BatchIntegrand), but saves having to update old code.

- The path-integral example is a little bit more organized.

- Ongoing polishing of documentation.

=============================
The last (probably) in a series of very minor changes. Here only the
documentation has been changed. There is a new section in the Tutorial
showing how to use multiple CPUs to evaluate costly integrands in parallel.
There is also a new section on how to use vegas to do multi-dimensional sums,
rather than integrals.

Also fixed errors in the documentation for random and random_batch generators.

============================
Another very minor (backwards compatibile) modification. Internally vegas processes
integration points in batches. These were called vectors initially but this name
has proven confusing, especially now that integrands can be array-valued.
To remove the potential confusion, collections of integration points are
now called batches, and: VecIntegrand is now BatchIntegrand; vecintegrand is
now batchintegrand; and nhcube_vec has become nhcube_batch. The old names
are still available, as aliases, to support legacy code.