Fix build with 0.13.0 and add support for zon

[redmaner]

As mentioned in the title:

• this fixes building on Zig 0.13.0
• this adds a build.zig.zon file and b.addModule to build.zig. These changes allow to import base32 module when fetching the dependency with zig fetch --save. Updated the README to include instructions on how to install using the zig package manager, since docs on the package manager are still pretty much non existent at this point.

[gernest]

@redmaner thanks, so we will also need to create 0.2.0 tag right ?

[redmaner]

@gernest would make sense, but it is not necessarily required as of now. It seems zig fetch basically ignores the whole package version for now that is set in zig.build.zon so when you fetch it like zig fetch --save git+https://github.com/gernest/base32 it will just resolve to the latest commit on the default branch, regardless of how you tagged it.

You can however also fetch specific tags. So if you would tag it as v0.2.0 you can fetch it as: zig fetch --save https://github.com/gernest/base32/archive/refs/tags/v0.2.0.tar.gz

[gernest]

Thanks, I just pushed v0.2.0 tag. It is safe to have stable tags.