Update benchmarking

[hugovk]

Changes proposed in this pull request:

• Remove little-used yajl (882 downloads in Feb), https://github.com/rtyler/py-yajl has been archived
• Add orjson and nujson
• Add handling for orjson's "recursion limit exceeded" for complex objects, just skips
• Comma separate thousands in the output for readability, and no need for 2 decimal places, the numbers are from the tens to the tens of thousands
• Update README with benchmarked data, using last ujson release, on Linux on GHA
• Benchmark dev version on pushes to master. Not other branches or PRs, because it can take up to 15 mins to run
• Could try on other Python versions and other operating systems too at some point