`Hash_t` supports sub-tags

[MikeKutz]

As a developer using Hash_t
I want to use sub-tags
because this is needed for other projects

sub-tag are like i.part and top.mid.bottom.tag

Results

• put_value() supports Hash_t
• get_hash() fetches a Hash_t
• get_*() supports sub-tags
• UT is updated

Dependent on #6

[MikeKutz]

Hash_t.get_*( key ) works with sub-keys implicitly.

I need to verify & test for put_*

[MikeKutz]

update: only get_string() properly supports sub-tags