Alpha release of 0.1.3

Bug fixes:

• Issue #2 on GitHub fixed. [commit] (562a4d3)
• The attributes of :class:fwdpy11.fwdpp_types.Mutation are now read-only, addressing Issue #5 on GitHub. commit

API changes/new features:

• :func:fwdpy11.util.change_effect_size added, allowing the "s" and "h" fields of :class:fwdpy11.fwdpp_types.Mutation to be changed. commit
• Trait-to-fitness mapping functions for quantitative trait simulations now take the entire population, rather than just the generation. This allows us to model things like truncation selection, etc. commit

Back-end changes

• :mod:fwdpy11.model_params has been refactored, addressing issue #4 on GitHub. The new code base is more idiomatic w.r.to Python's OO methods.commit
• Many of the C++-based types can now be pickled, making model parameter objects easier to serialize. Most of the
  changes are in this commit. This mostly addresses Issue #3 on GitHub.
• Added magic numbers to keep track of compatibility changes to serialization formats.
• str changed to repr for region types commit
• fwdpy11.model_params now uses try/except rather than isinstance to check that rates are float-like types.commit