macOS: add marketing name

[Shieldine]

This PR adds a lookup function on macOS marketing names.

Apparently, Apple does not expose this name at all (shame on Apple!), so a lookup function is the only way.

[barracuda156]

@Shieldine Unfortunately, if does not work. Building from 3b4632c I get this:

----------------------------------- OS ------------------------------------
Operating System:    macOS
version:             <unknown> (10K549)
kernel:              Darwin 10.8.0
architecture:        32 bit
endianess:           big endian

With my patch from #125 it was working correctly.

[Shieldine]

@barracuda156 that's because your version of MacOS can't be determined (version: <unknown>) and the marketing name is derived directly from that version. It'll work once your patch goes through and the version is displayed correctly