NPArrayBlobField SubfieldBase has been deprecated

[cboulay]

@mikkeyboi

I haven't used this in a while, but last time I did I got deprecation errors in my NPArrayBlobField due to its use of SubfieldBase.

Here (maybe) is the fix.

But while working on this, please take a look at this other example of how to make a numpy-compatible field in Django. They only bothered to get it working with PostgreSQL. The main difference is the database's backend data type.

Another idea: Maybe we should subclass SizedBinaryField instead.

[mikkeyboi]

Yes I had to replace SubfieldBase for the migration to work properly, along with the following files in this PR: #13

Operations to perform:
  Apply all migrations: admin, auth, contenttypes, sessions
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying admin.0002_logentry_remove_auto_add... OK
  Applying admin.0003_logentry_add_action_flag_choices... OK
  Applying contenttypes.0002_remove_content_type_name... OK
  Applying auth.0002_alter_permission_name_max_length... OK
  Applying auth.0003_alter_user_email_max_length... OK
  Applying auth.0004_alter_user_username_opts... OK
  Applying auth.0005_alter_user_last_login_null... OK
  Applying auth.0006_require_contenttypes_0002... OK
  Applying auth.0007_alter_validators_add_error_messages... OK
  Applying auth.0008_alter_user_username_max_length... OK
  Applying auth.0009_alter_user_last_name_max_length... OK
  Applying auth.0010_alter_group_name_max_length... OK
  Applying auth.0011_update_proxy_permissions... OK
  Applying sessions.0001_initial... OK

I'll take a look at working with numpy in Django and update this post.