Add support for citext columns in postgres 
I wouldn't say "incorrectly" -- Peewee does not have any field comparable to a case-insensitive text field. Pwiz is designed to cover the most common data-types but it cannot hope to cover them all. Hence, `UnknownField`. You can go through and replace them with `TextField` if you like.
 Aren't `text` and `citext` different, though? Isn't the real problem that peewee doesn't have a case-insensitive field?
 They are different, and yes, the issue is that peewee does not have a case-insensitive text field. That said, I don't plan on adding one. If you'd like you can add one yourself quite easily, though:

http://docs.peewee-orm.com/en/latest/peewee/models.html#creating-a-custom-field
 Is it as simple as,

    class CITextField(TextField):
        field_type = 'citext' That's all you need.
`pwiz` incorrectly translates `citext` columns to `UnknownField`.
