Update anti_ddos_challenge.lua

WAF Features added :
Added ability to inspect URL for malicious content SQL/SQI Injections XSS attacks / exploits.
Added ability to inspect query strings and arguements for malicious content / exploits.
Added ability to inspect all Request Headers provided by the client connecting.
Added ability to inspect cookies for exploits.

Marked of the TODO list : #29

Added Feature to pass IP to backend in existing headers like Cloudflare and Such CDN's do https://support.cloudflare.com/hc/en-us/articles/206776727-What-is-True-Client-IP-

Added Feature to modify headers on site URL's Paths Query Strings etc the reason for this is to strip out unwanted header values that could expose the software the server runs like the "Server" header and to add in custom headers to responses like to get clients to Cache files to save server / site bandwidth and resources.