Port Text prompt to return custom types parsed from the input

[mikaelmello]

CustomType prompts are basically a simplified version of Text prompts but with an additional generic type that we are parsing the input into.

As @rongcuid suggested on #72, this direction of extending Text capabilities might be a very good idea.

My main concern is in the UX aspect of it. I am afraid of bloating the Text prompt and making the common use-case too complicated for most users. The goal is to find a way to allow the addition of parsers, but exclusively in the form of new methods and that existing Text prompts wouldn't need a single character change to continue working as they currently are.