Some ruby gems where still in ruby-core pkg. These files where
moved outside ruby-core into ruby-gems or their own subpkg.

ruby-unit renamed to ruby-testunit as its gem is named test-unit.

ruby-rdoc left a file in ruby-core.

Psych is a gem and deserves its own subpkg. It replaces syck
(used by yaml) on recent ruby version (ref:
https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/36786)
Also, some psych files where packed incorrecly into ruby-json. The asterisk
in */json was intend to match <arch>/json/ and not psych/json.

Files where derived
from ruby-core and a lost file in ruby-json.

New subpkgs:
- ruby-bigdecimal
- ruby-io-console
- ruby-minitest
- ruby-psych

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>