Update README to begin workaround for go.dev bugs

Replaced a handful of markdown tables with SVG: "cbor speed/memory comparison", "cbor security comparison", "cbor features" and one more.

There's a lot of markdown tables remaining (encoding/decoding option tables, etc.) that are being rendered incorrectly on go.dev.

Mentioned the bug fix for v2.2, and CBOR  decoder settings: `MaxNestedLevels`, `MaxArrayElements`, `MaxMapPairs`, and `IndefLength`.

go.dev bugs filed about this are:
golang/go#37284
golang/go#37394

Closes #175