Massive updates to README.md

[kwwall]

I just made massive updates to our README.md file and lesser updates to SECURITY.md. There is also a new file named Vulnerabilty-Summary.md that is a summary of all the ESAPI Security Bulletins and GitHub Security Advisories relevant to ESAPI.

If you find anything egregiously wrong, please open a GitHub issue or do a PR to fix it. If it's just a minor typo / grammar error, just drop me an email and I'll clean it up the next time I am making changes.

Thanks,

-kevin