Asks the user for input.

Usage:

// Takes any input
$color = CLI::prompt('What is your favorite color?');

// Takes any input, but offers default
$color = CLI::prompt('What is your favourite color?', 'white');

// Will validate options with the in_list rule and accept only if one of the list
$color = CLI::prompt('What is your favourite color?', array('red','blue'));

// Do not provide options but requires a valid email
$email = CLI::prompt('What is your email?', null, 'required|valid_email');

@param string       $field      Output "field" question
@param string|array $options    String to a default value, array to a list of options (the first option will be the default value)
@param string       $validation Validation rules

@return             string                   The user input
@codeCoverageIgnore