Partial typing fix, add select_all, change model fields to instances

0.10.0

Breaking

• Dropped supported for long deprecated notation of field definition in which you use ormar fields as type hints i.e. test_field: ormar.Integger() = None
• Improved type hints -> mypy can properly resolve related models fields (ForeignKey and ManyToMany) as well as return types of QuerySet methods.
  Those mentioned are now returning proper model (i.e. Book) instead or ormar.Model type. There is still problem with reverse sides of relation and QuerysetProxy methods,
  to ease type hints now those return Any. Partially fixes #112.

Features

• add select_all(follow: bool = False) method to QuerySet and QuerysetProxy.
  It is kind of equivalent of the Model's load_all() method but can be used directly in a query.
  By default select_all() adds only directly related models, with follow=True also related models
  of related models are added without loops in relations. Note that it's not and end async model
  so you still have to issue get(), all() etc. as select_all() returns a QuerySet (or proxy)
  like fields() or order_by(). #131

Internals

• ormar fields are no longer stored as classes in Meta.model_fields dictionary
  but instead they are stored as instances.