ruby: move gems out of core

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
ruby: remove refs from dropped syck

syck was replaced by psych in yaml. (ref:
https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/36786)

Also add ruby-psych to ruby-yaml deps
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)
ruby: fix misplaced backslash (bad syntax)
ruby: add auxiliar scripts in order to help tests

ruby_find_pkgsdeps: look for file dependencies (checks
require and Encoding references) and extrapolate it to pkgs
deps. Also checks whether a dep is redundant or missing in pkgs.
Must run inside an OpenWRT with all ruby* pkgs installed.

ruby_missingfiles: list files in staging/target and from files
comparing side by side its contents. It helps to easly visualize
which file is not packaged in an ipk.
ruby: create subpkgs ruby-enc-extra from ruby-enc

Ruby encoding library was too big and bring unecessary encodings for a simple ruby usage.
All not directly required encodings from stdlib where moved to ruby-enc-extra.

Created pkg from ruby-enc
- ruby-enc-extra (from ruby-enc)
ruby: move files to ruby-xmlrpc,ruby-dl left in ruby-core

Some files that belong to other subpkgs where still in
ruby-core. Just moved them to the correct place.
ruby: fix missed ruby-testunit/install rename

From commit 1c5ef2e2ca6d59fae41ea0db1b8c42667b588221,
ruby-unit/install was not renamed to ruby-testunit/install.
So, no ipk was generated.
ruby: explode ruby-core into subpkgs

ruby-core is problematic as it is too big.
It is impossible to fix pkgs dependencies as
ruby-core would generate multiple cycled dependencies
between packages.

Also, "core" in ruby context means "classes that does not need a 'require'".
This is not the case of ruby-core classes. They are, actually, a subset of
Ruby Standard Library.

In every detected case where a portion of ruby-core could be isolated and
save another pkgs from requiring all ruby-core where spin-off into a new
subset. Also, big portions of ruby-core, not require by current ruby-* pkgs
where spin-off in new pkgs. The remaining of ruby-core was put into a new ruby-misc.

ruby-stdlib was created as a meta package that requires all ruby packages that are
part of Ruby Standard Library. For a full Ruby Standard Library, just install
ruby-stdlib and its deps.

Created pkgs from ruby-stdlib:
- ruby-misc
- ruby-csv
- ruby-datetime
- ruby-dbm
- ruby-debuglib
- ruby-drb
- ruby-fiddle
- ruby-filelib
- ruby-logger
- ruby-math
- ruby-multithread
- ruby-mkmf
- ruby-net
- ruby-optparse
- ruby-patterns
- ruby-prettyprint
- ruby-pstore
- ruby-racc
- ruby-rbconfig
- ruby-rinda
- ruby-ripper
- ruby-sdbm
- ruby-shell
- ruby-socket
- ruby-uri

Some files from ruby-openssl where moved to new subpkgs (as ruby-net and ruby-drb).

All dependencies where redefined based on auxiliar script ruby_find_pkgsdeps
ruby: update to 2.1.3