Implement additional textfield and textarea attributes

This includes:

1. The proposed `keyboard` attribute at https://github.com/Jasonette/documentation/issues/72
2. And some of the missing attributes that haven't been added to Android side yet, which includes: `autocorrect`, `autocapitalize`, and `spellcheck`.

Start by locating the Android implementations for textfield and textarea and compare their existing attributes with the linked documentation issue #72. Check how keyboard, autocorrect, autocapitalize, and spellcheck are represented, then verify that each requested attribute is supported on Android and covered by the relevant tests, if present.

Written by the indexing model from the issue text.