Type constraints are stored in @KURA

[kfly8]

This pull request provides the method get type constraints list, it is useful for exporting type constraints by %EXPORT_TAGS. Here is an example code:

    package MyBar {
        use Exporter 'import';
        use Types::Common -types;
        use kura Bar1 => StrLength[1, 255];
        use kura Bar2 => StrLength[1, 1000];

        our %EXPORT_TAGS = (
            types => \@MyBar::KURA,
        );
    }

    use MyBar qw(:types);
    # => Bar1, Bar2 are exported