sysvmq: edition C

Here's the C attempt from today, since fuck FFI. I've benchmarked this and it's webscaler than what we use right now, it's maintainable, doesn't hold the GVL when doing blocking calls, etc.

Still a lot of things to be done, but this can be a 0.0.1.

@Shopify/stack, since that doesn't work:
@wvanbergen @burke @justinplouffe @graemej

@camilo and @csfrancis since we talked about this today.