ruby: spin-off ruby-digest from ruby-openssl

ruby: spin-off ruby-digest from ruby-openssl

Digest can use OpenSSL or ruby internal implementation of hash functions. The first
uses less disk space but requires openssl, that is relatively big. As internal hash
implementations are not too much bigger than openssl version, it is compiled by
default. A new config option can change it to use OpenSSL instead.

As digest is independent from openssl, ruby-digest was created as a new pkgs.

Adds pkgs:
- ruby-digest (from ruby-openssl)

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