update build.zig for zig 0.12.0-dev.3635+786876c05

[tazend]

Hi,

first off: thanks for this library, tried it out in one of my projects and it works pretty nice.

I'm using pretty much the latest zig on my project right now (zig 0.12.0-dev.3635+786876c05), and there were some errors while building.

1. Passing target to the buildExamples function which requires a std.zig.CrossTarget type doesn't work (anymore). It throws this error:

expected type 'Target.Query', found 'Build.ResolvedTarget'

Instead I just changed it to require std.Build.ResolvedTarget. Not really sure if this is the right way, but it builds.

2. Make the "prettytable" module available for other projects to import as a dependency.

Without this:

const module = b.addModule("prettytable", .{
    .root_source_file = .{ .path = "src/lib.zig" },
});

it is not possible to import prettytable inside of other projects depending on it. It worked for the examples because there it was added as a private module to them (createModule only creates a private module). With the lines above however, importing it in external projects works.
Additionally, this can just be passed on to the buildExamples function and used as module for the examples, removing the need to call createModule again.

3. Other than the above, just a few things that weren't needed anymore have been removed, like FileSource (which was recently renamed to LazyPath in zig), Builder and CrossTarget

[Hanaasagi]

Thank you for this. I appreciate your taking the time to explain the changes in the recent Zig version.