feat: support BROWSER env var in Linux

[bjones1]

Per #108, this PR adds support for the BROWSER environment variable in Linux.

I've also added a Codespaces config file, which allowed me to test this easily in Codespaces.

Feedback is welcome!

[Byron]

Apologies, but I realize this issue came up before: #8 .
There I predicted that implementing this correctly wouldn't be easy, and that it would be a major version change if put into the belly of the that() function.

However, you could add a new function that tries BROWSER first to basically open everything, then fallback to the other programs.

If this sounds like too much, I'd happily take the codespaces configuration commit.

[Byron]

Just to put this PR into the right state.

[bjones1]

Per the docs for this crate, "Use this library to open a given path or URL in some application, obeying the current user’s desktop configuration." After reading #8, I think that there's no good way to accomplish this goal on Linux -- ignoring $BROWSER causes some cases to fail, while using $BROWSER causes other cases to fail. Per #8, I think that encouraging users to use the webbrowser crate if the purpose is to open a URL in a web browser is best, instead of adding more functions that are web browser only. Therefore, I'd suggest closing this PR and instead updating the docs to clarify this point.

I'll submit the Codespaces update as a separate PR.

What are your thoughts?

[Byron]

Therefore, I'd suggest closing this PR and instead updating the docs to clarify this point.

Yes, that sounds good. I hope you will find the time to contribute that addition as well, and agree that referring this to the webbrowser crate is preferable.

Thanks again!