Prompts: Support different field types

[Taitava]

Discussed in #17

I'm going to create at least the following new field types:

• A multiline text field.
• On/off toggles (aka checkboxes). These need to have a definition for two texts: a text when the toggle is on, and a text when the toggle is off. *
• A dropdown list of predefined options. Allows one item to be selected.
• A password field.

For other planned field types, please see the discussion #17 . There's more field types that will be implemented later.

Other things:

• Write documentation for password field.
• Write documentation for other fields.
• Create tests.
• Add to changelog.