gitignore: mac

ignore .DS_Store
formalize: Force types.

Formalize will return a default input for each fieldtype. These
functions will make it possible to force another type than the default.
formalize: Valid types

When forcing types the types must be valid for the type of input.
formalize: Process length

Fetch values from the length field. This enables getting max length of
strings and integer and possible values for set and enum. There should be an
easier way of doing this so I might change it later.