updates StringArray to use TEXT primitive

The current implementation of `StringArray` uses `VARCHAR` and seems undesirable for any real world use. Further more, the postgresql docs use `TEXT` in its [examples](http://www.postgresql.org/docs/9.3/static/arrays.html), and I believe svs/dm-pg-types should follow suit.

This change re-implements `StringArray` to use `TEXT` and drops the length option entirely. If this is too heavy handed, let me know, and I will re-submit with a new type, `TextArray`, so that the old implementation can be left as is, but I feel strongly that `StringArray` is unfit for service, and so took this approach first.

Thanks!