Release 3.0.0: modernize for Ruby 3.4/4.0

[kennym]

Summary

Brings this gem from the 2014 Jeweler/Travis/Ruby 1.9 stack to a current Ruby library, and confirms the Ideone SOAP API still works.

• Require Ruby 3.4+ (developed on 4.0)
• Replace Jeweler with a maintained gemspec; replace Travis with GitHub Actions (3.4 and 4.0)
• Call Ideone over HTTPS (https://ideone.com/api/1/service.wsdl)
• Upgrade Savon to ~> 2.17 and add cgi (needed on Ruby 4)
• Minitest 6 + WebMock unit tests; optional live tests via IDEONE_USER / IDEONE_PASSWORD
• README rewritten (language ids, status/result codes, development)

Live SOAP checks on 2026-09-19: testFunction, getLanguages (id 17 is still Ruby), createSubmission, getSubmissionStatus, and getSubmissionDetails all succeeded.

Breaking changes

• Ruby < 3.4 is no longer supported
• Non-auth Ideone errors now raise Ideone::Error instead of Ideone::AuthError
• Default WSDL is HTTPS

Test plan

• bundle exec rake on Ruby 4.0.7
• bundle exec rake on Ruby 3.4.10
• Live Ideone create/status/details through the new client
• GitHub Actions CI on this PR