#11: removed references to `usingnamespace`

[Voxi0]

Zig 0.15 removed usingnamespace due to the reasons explained in issue https://github.com/ziglang/zig/issues/20663.

In order to use a newer version of Zig (0.14+) it's necessary to remove references to usingnamespace to avoid compile-time syntax errors duh.

However doing so means that some things had to be slightly renamed sadly. I couldn't really find another way around it but it's only some slight renaming which shouldn't be too hard.

If any of you have better name suggestions or noticed I forgot to document some change or something then let me know.

I've tested my OS again and now I can finally compile with Zig 0.16-dev without any issues. I haven't tested all my individual changes though so keep that in mind, though I'm sure everything would work fine after some slight renaming.

Changes-

• Term -> Holds TerminalRequest and TerminalResponse (Deprecated Limine feature)
• Paging -> Holds FiveLevelPagingRequest (Deprecated Limine feature)
• FileFeature -> Holds ExecutableFileRequest and KernelFileRequest (For older Limine API)
• MultiprocessorFeature -> Holds MpRequest and SmpRequest (For older Limine API)
• Removed KernelAddressFeature, just use ExecutableAddressFeature instead, the structs have the same properties anyways so it's a drop-in replacement.
• BootTimestampFeature -> Holds DateAtBootFeature and BootTimeFeature (For older Limine API)

[Voxi0]

I'll continue to use my fork until this gets merged or something.