add platform-specific issue/PR labels

[misterdjules]

As discussed in the PR that documented supported platforms, I'd like the libuv project to add platform-specific issue/PR labels for all supported platforms, and libuv collaborators to use these labels when an issue/PR is specific to one or more of these platforms.

The primary motivation for me is to make searching through SmartOS specific issues/PRs easier, so that I can check periodically for those that require my attention.

[bnoordhuis]

I added a few labels and gave them the same name and colors as their nodejs/node counterparts.

nodejs/node only seems to have 'solaris', not 'smartos', so I followed that here but feel free to create one.

[misterdjules]

I added a few labels

Thank you!

nodejs/node only seems to have 'solaris', not 'smartos', so I followed that here but feel free to create one.

It seems I don't have permissions to create labels, probably because I'm not part of any team with access to the libuv/libuv repository.

[bnoordhuis]

Okay, added a smartos label. The color was scientifically derived with echo -n smartos | sha1sum | cut -b1-6.

I added a 'linux' label using the same process because apparently we didn't have one. I'll close but let me know if anything else needs to be done.