Ideas from Pydantic

I'm currently exploring integration between Param and Pydantic.

I will use this issue to highlight some things Param could learn or otherwise utilize from Pydantic.

## 1. Pydantic is compiled with Cython to make it super fast.

Could/ should Param be?

## 2. Pydantic has a very fast and flexible deserialization

Could Param inherit that code just as Pydantic inherited from Django? For example for `int` it will deserialize both 123 and "123" to 123. For example for datetimes it can deserialize a wide range of formats.

For example for parsing datetime https://github.com/samuelcolvin/pydantic/blob/master/pydantic/datetime_parse.py.