TabixReader implements Autoclose

[lindenb]

Description

I added AutoCloseable to TabixReader so it can be used in a try-with-resource statement.

Things to think about before submitting:

• [x] Make sure your changes compile and new tests pass locally.
• [x] Add new tests or update existing ones:
  • A bug fix should include a test that previously would have failed and passes now.
  • New features should come with new tests that exercise and validate the new functionality.
• [ ] Extended the README / documentation, if necessary
• [x] Check your code style.
• [x] Write a clear commit title and message
  • The commit message should describe what changed and is targeted at htsjdk developers
  • Breaking changes should be mentioned in the commit message.