I've been avoiding using 'bool', instead I'll use 'int',

One reason is I feel unsafe to print the default value, not sure if there are environment such that boolalpha is on by default, then users will see 'true' or 'false' as the default values, but `--no_drm true` is not accepted.

Another is that there could be multiple values in the future, also I want to restrict the data types to int/double/string only, such that it will be relief for templates in ArgParser