add support for Illumos

[siepkes]

This commit introduces support for Illumos, an (Open) Solaris derivative.

uname -o on Illumos returns illumos.

It also clarifies the documentation a bit on why the domainname field is missing for OS'es like the BSD's and Illumos.

[codecov]

Codecov Report

Merging #48 (343298f) into main (6a66620) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
+ Coverage   94.97%   94.98%   +0.01%     
==========================================
  Files           4        4              
  Lines         956      958       +2     
==========================================
+ Hits          908      910       +2     
  Misses         48       48              

Flag	Coverage Δ
macos_latest	99.33% <100.00%> (+<0.01%)	⬆️
ubuntu_latest	99.33% <100.00%> (+<0.01%)	⬆️
windows_latest	94.49% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/platform/unix.rs	99.03% <100.00%> (+0.01%)	⬆️

[siepkes]

It seems Github actions dies on a style check in an integration test. Oddly enough this PR doesn't change that code. I think the style check might have been updated? Causing it to suddenly fail on this piece of existing code?

error: redundant clone
  --> tests/integration_test.rs:51:25
   |
51 |     let info_copy = info.clone();
   |                         ^^^^^^^^ help: remove this
   |
note: cloned value is neither consumed nor mutated
  --> tests/integration_test.rs:51:21
   |
51 |     let info_copy = info.clone();
   |                     ^^^^^^^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone
   = note: `-D clippy::redundant-clone` implied by `-D warnings`

error: could not compile `platform-info` (test "integration_test") due to previous error
warning: build failed, waiting for other jobs to finish...
error: redundant clone

[rivy]

Hmm, odd that it didn't show up as failures in the prior merge with the CI code change.
I'll fix it and you can rebase onto the new 'main'.

[rivy]

Minor nit... we generally use active/imperative voice for commit messages.
When you rebase onto the new 'main', would you mind changing the commit message to "add support for Illumos"?

[rivy]

@siepkes , the updated 'main' is now available. If you rebase, I expect that all tests should pass.

[siepkes]

Your changes seem to have worked. All checks passed!