Change updateSnap to look for the file in src/ if it exists

[jullanggit]

Solves #2, by looking for files in src/ if it exists. If there is no src/ directory, it looks in the cwd like before.
I think this is an acceptable solution, as project files are to my knowledge basically always in src/ if it exists.
If this isn't the case or this solution is too hacky, I would be happy to improve it, although I would need a bit of guidance as I have no idea how to properly get the root module's directory

[mnemnion]

This is too hacky for me, but, you've given me an idea.

If, instead of just trying for the /src directory, we had a config in build.zig which defaults to the /src directory, but which can be configured for unusual cases by the user, that might be sufficient.

I still think it would be a pity if 0.14 shipped without any way to open a file given the result of calling @src(), but it's time to start planning for that possibility.

The solution might need to be slightly more involved than that, because since it's possible to have, for instance, ./src and ./test directories which both use ohsnap, I'd like the configuration to support that possibility. That's solvable with an a-list-like structure, something like [][2][]const u8, with [0] as the module name and [1] as the directory, defaulting to "root", "./src".

I'll need some time to take a look at the Zig issue board, maybe talk to some people, but this seems like a reasonable Plan B. It would live in the build file and otherwise be set-and-forget, which is acceptable.