Clean up state on context timeout/cancellation

[jhendrixMSFT]

Document the potential for connection errors. This required refactoring the link closing code. It now follows the same pattern as Session.

• [ ] The purpose of this PR is explained in this or a referenced issue.
• [ ] Tests are included and/or updated for code changes.
• [ ] Updates to CHANGELOG.md are included.
• [ ] MIT license headers are included in each file.

[jhendrixMSFT]

Partial fix for https://github.com/Azure/go-amqp/issues/246