feat: Expand platform support

[umgefahren]

This PR introduces better support for Tier2 and Tier3 (apple) targets including:

• macOS
• iOS
• watchOS
• tvOS
• visionOS
• FreeBSD
• NetBSD
• OpenBSD

Resolves: #42

The CI was updated to reflect more modern practices, while compile tests for the new platforms where added.

Additionally now cfg flags are visible in docsrs through the introduction of nightly only, but available on docs.rs, documentation.

[messense]

LGTM, thanks a lot!

[SludgePhD]

This PR broke the docs.rs build of if-addrs. It is now complaining about a cfg directive because it is missing a ,:

[INFO] [stderr] error: expected one of `)` or `,`, found `not`
[INFO] [stderr]    --> src/lib.rs:437:9
[INFO] [stderr]     |
[INFO] [stderr] 436 |         not(target_os = "netbsd")
[INFO] [stderr]     |                                  -
[INFO] [stderr]     |                                  |
[INFO] [stderr]     |                                  expected one of `)` or `,`
[INFO] [stderr]     |                                  help: missing `,`
[INFO] [stderr] 437 |         not(target_os = "openbsd")
[INFO] [stderr]     |         ^^^ unexpected token

[umgefahren]

This PR broke the docs.rs build of if-addrs. It is now complaining about a cfg directive because it is missing a ,:

[INFO] [stderr] error: expected one of `)` or `,`, found `not`
[INFO] [stderr]    --> src/lib.rs:437:9
[INFO] [stderr]     |
[INFO] [stderr] 436 |         not(target_os = "netbsd")
[INFO] [stderr]     |                                  -
[INFO] [stderr]     |                                  |
[INFO] [stderr]     |                                  expected one of `)` or `,`
[INFO] [stderr]     |                                  help: missing `,`
[INFO] [stderr] 437 |         not(target_os = "openbsd")
[INFO] [stderr]     |         ^^^ unexpected token

Thank you so much for finding that, I'm really sorry I caused that. I have opened #45 introducing a fix and bumping the version allowing for new publishing on crates.io.