Mk/**ruby.mk: Switch from USE_RUBY=yes to USES=ruby

Switch from Mk/bsd.ruby.mk to Mk/Uses/ruby.mk

Notable changes are.

- Mk/bsd.ruby.mk is moved to Mk/Uses/ruby.mk.
- USE_RUBY=yes is replaced with USES=ruby.
- USE_RUBY_EXTCONF is replaced with USES=ruby:extconf.
- USE_RUBY_RDOC is replaced with USES=ruby:rdoc.
- USE_RUBY_SETUP is replaces with USES=ruby:setup.
- RUBY_NO_BUILD_DEPENDS and RUBY_NO_RUN_DEPENDS are replaced with
  USES=ruby:{build,none,run}.
- RUBY_REQUIRE isn't used anywhere, so removed.
- USES=gem now implies USES=ruby.

This is mainly the work of yasu@ at https://reviews.freebsd.org/D27863

I have just made some cosmetic changes and ran exp-run to test that the
tree is not in a BROKEN state.

Approved by:	portmgr
Differential Revision:	https://reviews.freebsd.org/D37925

Remove WWW entries moved into port Makefiles

Commit b7f05445c00f has added WWW entries to port Makefiles based on
WWW: lines in pkg-descr files.

This commit removes the WWW: lines of moved-over URLs from these
pkg-descr files.

Approved by:		portmgr (tcberner)

Add WWW entries to port Makefiles

It has been common practice to have one or more URLs at the end of the
ports' pkg-descr files, one per line and prefixed with "WWW:". These
URLs should point at a project website or other relevant resources.

Access to these URLs required processing of the pkg-descr files, and
they have often become stale over time. If more than one such URL was
present in a pkg-descr file, only the first one was tarnsfered into
the port INDEX, but for many ports only the last line did contain the
port specific URL to further information.

There have been several proposals to make a project URL available as
a macro in the ports' Makefiles, over time.

devel/rubygem-rails-i18n-rails50: Update to 5.1.3

Changes:	https://github.com/svenfuchs/rails-i18n/blob/master/CHANGELOG.md

One more small cleanup, forgotten yesterday.
Reported by:	lwhsu

Remove # $FreeBSD$ from Makefiles.

Update version requirement of RUN_DEPENDS

Update to 5.1.2

Changes:	https://github.com/svenfuchs/rails-i18n/blob/master/CHANGELOG.md

Update to 5.1.1

Changes:	https://github.com/svenfuchs/rails-i18n/blob/master/CHANGELOG.md

Update to 5.1.0

Changes:	https://github.com/svenfuchs/rails-i18n/blob/master/CHANGELOG.md

Set ruby@FreeBSD.org as maintainer of these ports, so that ruby team can
more easily contribute to their maintenance.

devel/rubygem-rails-i18n-rails50: Create rails version 5.0 port by copying
devel/rubygem-rails-i18n

Approved by:	swills (mentor, implicit)