v0.4.0

[0.4.0] - 2020-07-25

Added

• Schema.__getitem__() implementation to get a schema field programmatically.
• Schema.get_all_fields() to recursively get all the fields and nested fields from a schema.

Changed

• The Schema fields are now stored in an OrderedDict so that the original order that the fields
  were added to the Schema is preserved when tterating over the Schema's fields, via iter() or
  the new get_all_fields().