Add "Last Stable release" column to table

[seghcder]

Many thanks for the work to benchmark these!

One of the most important criteria for evaluating frameworks to use is whether the package is actively maintained, and the quality of that maintenance.

I think it would help greatly to add "Last Stable Release" to your table in this section. https://github.com/guteksan/REST-CPP-benchmark#other-aspects, or some other factor to reflect this.

Also, cross-platform support would be a useful nice to have.