Fwdpy11

This is an intermediate release as we are still working towards supporting more general demographic models.

Major changes include:

* Updating the fwdpp back-end to the pre-release code for fwdpp 0.8.0. Almost none of these changes are "user facing".
* Add :class:`fwdpy11.SiteTable`, :class:`fwdpy11.Site` and new fields to :class:`fwdpy11.MutationRecord`. 258 These changes affect the API for some function calls. See :ref:`upgrade_path` for details.

Even though this release changes some of the tree sequence data structures, we are still able to read in files generated by version 0.4.5! (This is actually unit tested.)

Minor changes include:

* Add :func:`fwdpy11.gsl_version`. :class:`fwdpy11.MutationRecord`.256
* :attr:`fwdpy11.Mutation.g` is converted to the mutation's age when dumping table collections to tskit's format. 257
* New exception types from fwdpp registered as Python exceptions. 260
* Several updates to documentation and to continuous integration testing.

Fixes handling of nested window coordinates. 244

Added `fwdpy11.DataMatrixIterator`, which allows very fast traversal of multiple genomic intervals, retrieving the genotype matrix at each window.

* Minor fixes to packaging of source distrubition.
* Add a YCM config file to source repo
* Allow mutation and recombination regions to be empty. [PR 239](https://github.com/molpopgen/fwdpy11xx/pull/239)

VariantIterator's `__init__` now accepts arguments to skip neutral or selected variants.

Minor release:

* Added position ranges to tree traversal. 232
* Changed default type for range arguments for VariantIterator and data matrix generation. 233
* Skipping fixations is now optional in :func:`fwdpy11.data_matrix_from_tables`.
* The C++ back-end for population classes was changed to avoid deleting move constructors. 231
* Documentation updates