Reorganize and improve go code

[WillAbides]

When working on #476 I noticed that Go benchmarks are a tough to work on because they are all in the same directory so editors interpret that as one big package with a lot of duplicate function names.

I propose changing the layout of the Go benchmarks to be more like the Rust layout. There would be a common/go package with a Run function that runs the benchmarked function and sends the results to :9001.

Each test directory would have a test-go subdirectory that contains a separate package for each Go benchmark. For example there would be json/json-go/goccy and json/json-go/jsoniter.

If this gets a 👍 I can do the work. I did a little bit of exploratory work with a few json benchmarks, and it won't take too long to apply that to the rest of the Go benchmarks.

[nuald]

It's totally fine to reorganize the source code, especially considering how Go modules work. I guess after that we could finally drop GO111MODULE=auto, and please feel free to do that within you changes if you want.

Thanks for contributing!