Diesel-Async 0.7.4

What's Changed

• Keep track of mysql statements to close by @weiznich in #271

Full Changelog: v0.7.3...v0.7.4

You can support the development of Diesel by:

• Contributing Code, Documentation or Guides. Checkout the planing for Diesel 2.4 for open tasks.
• Providing knowledge and help to maintain the MySQL/MariaDB backend. This is currently the only in-tree backend that is not used by any maintainers, so having someone around that actually uses this backend would be very helpful for the Diesel project.
• Answering questions in our discussion forum
• Reporting bugs in our issue tracker
• Helping triaging issues in our issue tracker
• Sponsoring the maintainers.