Pyabc

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* Monitor code quality using codacy and codecov.
* Extend visualization routines: Add histogram, sample number, epsilon
trajectory, model probability, and credible interval plots.
* Test visualization routines on travis.
* Fix problem with the History.get_weighted_distances function after update to
sqlalchemy>=1.3.0.
* Add random walk based transition for discrete parameters.

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* Tidy up returning of rejected samples in Sample (not only summary
statistics).
* Recreate a population from file in History.get_population().
* Speed up loading from database by eager loading.
* Document the change of the contribution scheme to master+develop.

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* Allow for the database to save no summary statistics for testing purposes.
* Tidy up some pyabc.History methods.
* pyabc.History.id set by default to the largest index (previously 0),
corresponding to the latest inserted analysis.

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* Fix several errors with the readthedocs (rtd) documentation.
* Speed-up rtd build by removing unnecessary conda and pip requirements.
* Clean-up requirements for travis and rtd.
* Change rtd design from alabaster to sphinx_rtd_theme since it implements
better navigation.

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* ABCSMC can pass observed summary statistics to distance functions
(required for some scale functions, and to make the
methods robust to volatile summary statistics).
* Implementation of more scale functions (distance_functions.scales), in
particular some taking into account the bias to the observed data.
* AdaptivePNormDistance accepts a Callable as scaling scheme, allowing
for more flexibility.

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* Can specify kde and number of bins for all visualization routines.
* Can re-submit observed sum stats to ABCSMC.load() function in case
it cannot be read correctly from the db.