Crates.io bimap version needs to be updated

[billyrieger]

I released bimap version 0.4.0 on crates.io nearly a year ago. Since then there have been numerous improvements, mostly from other project contributors, and I'm both thankful for everyone's work and regretful that releasing your work has taken me this long. The good news is that I set a deadline for the release of version 0.5.0 to occur on July 31 - to commemorate when version 0.4.0 was released - but there are things I want to get done before that happens. An incomplete list of tasks is below (and the release will happen regardless of whether I accomplish any of them :sweat_smile:).

• [x] Fix the README and other public documents. Add issue templates and other community items.
• [x] Set up to continuous integration to build, test, and format pull requests. Being able to automate deployments would also be nice for me.
• [x] Clean up the codebase itself.
• [x] Create, populate, and maintain a changelog.

[billyrieger]

Not everything is 100% done, but it's good enough for me right now.