Extra configuration options for text fields

Hi Nick,

I am not an iOS developer but I created a new Root.plist file with the latest Xcode and checked the `AutocapitalizationType` setting. It looks like the *C* in *capitalization* is not capitalized, oh, irony. So, here you go, first minor change.

Secondly I added a `secure`, `keyboard`, `autocapitalization` and `autocorrection` option. All options default to the values you specified earlier. This should make the field configuration somewhat more flexible.

I needed a secure password field and prefer the *EmailAddress* keyboard for my e-mail field. You can now add those options when defining text fields:

    bundle.text "E-mail", key: "email", keyboard: "EmailAddress", autocapitalization: "None"
    bundle.text "Password", key: "password", secure: true