Improve and document Ruby support in 'etags'

Improve and document Ruby support in 'etags'

* lib-src/etags.c (Ruby_suffixes): Add ".ruby".
(Ruby_functions): Support "module" and overloaded operators.
(Ruby_help): Mention "module".

* test/etags/ruby-src/test.rb:
* test/etags/ruby-src/test1.ruby: New files.
* test/etags/Makefile (RBSRC): New tests.
(SRCS): Add ${RBSRC}.
* test/etags/ETAGS.good_1:
* test/etags/ETAGS.good_2:
* test/etags/ETAGS.good_3:
* test/etags/ETAGS.good_4:
* test/etags/ETAGS.good_5:
* test/etags/ETAGS.good_6:
* test/etags/CTAGS.good: Adapt to the new Ruby tests.

* doc/man/etags.1: Mention Ruby support.
* etc/NEWS: Mention Ruby support.