Pydantic

* fix tests for Python 3.8, [396](https://github.com/pydantic/pydantic/pull/396) by samuelcolvin
* Adds fields to the `dir` method for autocompletion in interactive sessions, [398](https://github.com/pydantic/pydantic/pull/398) by dgasmith
* support `ForwardRef` (and therefore `from __future__ import annotations`) with dataclasses, [397](https://github.com/pydantic/pydantic/pull/397) by samuelcolvin

* **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](https://github.com/pydantic/pydantic/pull/388) by samuelcolvin
* **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](https://github.com/pydantic/pydantic/pull/389) by dgasmith
* add `py.typed` marker file for PEP-561 support, [391](https://github.com/pydantic/pydantic/pull/391) by je-l
* Fix `extra` behaviour for multiple inheritance/mix-ins, [394](https://github.com/pydantic/pydantic/pull/394) by YaraslauZhylko

* Support `Callable` type hint, fix [279](https://github.com/pydantic/pydantic/pull/279) by proofit404
* Fix schema for fields with `validator` decorator, fix [375](https://github.com/pydantic/pydantic/pull/375) by tiangolo
* Add `multiple_of` constraint to `ConstrainedDecimal`, `ConstrainedFloat`, `ConstrainedInt`
and their related types `condecimal`, `confloat`, and `conint` [371](https://github.com/pydantic/pydantic/pull/371), thanks StephenBrown2
* Deprecated `ignore_extra` and `allow_extra` Config fields in favor of `extra`, [352](https://github.com/pydantic/pydantic/pull/352) by liiight
* Add type annotations to all functions, test fully with mypy, [373](https://github.com/pydantic/pydantic/pull/373) by samuelcolvin
* fix for 'missing' error with `validate_all` or `validate_always`, [381](https://github.com/pydantic/pydantic/pull/381) by samuelcolvin
* Change the second/millisecond watershed for date/datetime parsing to `2e10`, [385](https://github.com/pydantic/pydantic/pull/385) by samuelcolvin

* Fix to schema generation with `Optional` fields, fix [361](https://github.com/pydantic/pydantic/pull/361) by samuelcolvin

* add `ConstrainedBytes` and `conbytes` types, [315](https://github.com/pydantic/pydantic/pull/315) Gr1N
* adding `MANIFEST.in` to include license in package `.tar.gz`, [358](https://github.com/pydantic/pydantic/pull/358) by samuelcolvin

* **breaking change**: don't call validators on keys of dictionaries, [254](https://github.com/pydantic/pydantic/pull/254) by samuelcolvin
* Fix validators with `always=True` when the default is `None` or the type is optional, also prevent
`whole` validators being called for sub-fields, fix [132](https://github.com/pydantic/pydantic/pull/132) by samuelcolvin
* improve documentation for settings priority and allow it to be easily changed, [343](https://github.com/pydantic/pydantic/pull/343) by samuelcolvin
* fix `ignore_extra=False` and `allow_population_by_alias=True`, fix [257](https://github.com/pydantic/pydantic/pull/257) by samuelcolvin
* **breaking change**: Set `BaseConfig` attributes `min_anystr_length` and `max_anystr_length` to
`None` by default, fix [349](https://github.com/pydantic/pydantic/pull/349) in [#350](https://github.com/pydantic/pydantic/pull/350) by tiangolo
* add support for postponed annotations, [348](https://github.com/pydantic/pydantic/pull/348) by samuelcolvin