Fix special chars rendering in help default values

[yannoff]

Actual

Special characters like \n or \t are evaluated at help default values display, which is not what we want.

Example:

Usage
        bin/phpdoc.php ls:namespace [options] [--] 
Description
        List all the autoloaded classes namespaces, optionally filtered by a top namespace prefix
Options
        -h, --help         Display this help message
        --root-ns VALUE    Root Namespace: apply a prefix filter on namespace (default: Yannoff)
        --autoload VALUE   Optional override for the autoload file (default: vendor/autoload.php)
        -e, --exclude      A list of classes to exclude from documentation
        --ifs VALUE        Character used for joining items in output (default: 
)
        --fmt VALUE        Optional formatting string for items.

Expected

Values should appear in help message as "\n" or "\t"