group and annotate libraries that target a common encoding

[mumbleskates]

here's some logic I thought about to present the benchmarked libraries that target the same encoding (like json, cbor, protobuf etc.) more clearly, grouped together and clearly marked in the readme output. It looks like this

there's room to quibble about how this is presented; i just put like "json:<br>" before the crate in the first column of the table, but there's an argument to be made that maybe we could stick like a full-width table cell heading that just says "json" in it, though i'm not sure if that would really look better, and it doesn't seem like github flavored markdown supports merged cells anyway.

[finnbear]

Nice; however, I think you missed some in the README:

• https://github.com/near/borsh is a standard format
• https://crates.io/crates/minicbor (another CBOR)
• https://capnproto.org/ is a standard format
• https://github.com/google/flatbuffers is a standard format

[mumbleskates]

• borsh, capnp, and flatbuffers have no competitors. we could give them names though :)
• minicbor is technically cbor, but it's doing something significantly different than the other cbor encodings: it's using the cbor format as a carrier for a protobuf-style numerically surrogate keyed encoding rather than outputting field names and so on; this is part of why it's so much faster, and why i argue that it doesn't count as competing with the other cbor libraries and wouldn't necessarily be something you would choose if you needed to read & write cbor data.