Pyabc

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* Fix serious memory problem resulting from pickling more than necessary
for parallel sampling.
* Update logo, readme.
* Make tidying optional in abc-export (default behavior not changed).

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* Minor error and warning fixes due to API changes in pandas, seaborn (not
used any more), and change of the R installation on travis.

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* Default visualizations like plot_kde_matrix() can plot reference values,
useful for testing purposes.

..........

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* Acceptance transferred to an Acceptor object to allow for more
flexibility (i.e. not only on a single comparison as per default).
* This acceptor is passed to the ABCSMC object.
* Update of distance and epsilon synchronized after each iteration and moved
to update() methods.
* initialize() for DistanceFunction and Epsilon also called in load() method,
given a time point to initialize for, and made optional via a
require_initialize flag. This makes sure these objects are always correctly
initialized.
* PNormDistance and AdaptivePNormDistance (prev. WeightedPNormDistance)
improved to allow for more customization.
* ABCSMC.set_data() method removed.
* API breaks for DistanceFunction, Epsilon, Model.

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* Implementation of adaptive distances feature. Distance functions can adapt
via an update() method.
* In particular add WeightedPNormDistance (special case:
WeightedEuclideanDistance). Also add non-weighted versions.
* Simplify Sampler.sample_until_n_accepted interface.
* Extend Sampler class to allow for customization, e.g. by the distance
functions.
* Generalize MedianEpsilon to QuantileEpsilon.
* Make Viserver work with latest bokeh version.