update HISTORY.rst ready for release
History
-------
-v0.20.0 (unreleased)
-....................
+v0.20.0a1 (2019-02-13)
+......................
* **breaking change** (maybe): more sophisticated argument parsing for validators, any subset of
``values``, ``config`` and ``field`` is now permitted, eg. ``(cls, value, field)``,
however the variadic key word argument ("``**kwargs``") **must** be called ``kwargs``, #388 by @samuelcolvin
-* Adds ``skip_defaults`` argument to ``BaseModel.dict()`` to allow skipping of fields that were not
- explicitly set, #389 by @dgasmith
+* **breaking change**: Adds ``skip_defaults`` argument to ``BaseModel.dict()`` to allow skipping of fields that
+ were not explicitly set, signature of ``Model.construct()`` changed, #389 by @dgasmith
+* add ``py.typed`` marker file for PEP-561 support, #391 by @je-l
* Fix ``extra`` behaviour for multiple inheritance/mix-ins, #394 by @YaraslauZhylko
v0.19.0 (2019-02-04)
