Increase QPS in HTTP handler

[venediktov]

currently connection is non-persistent runs 11K QPS on a 4 core CPU 2.2Ghz Preliminary tests with updated CRUD showing major speed improvement tested by ab.sh --test it ran at 49K QPS .

• add persistent_connection.hpp to CRUD and use it in exchange_server<Handler,Connection>

[venediktov]

Waiting for approval from the team

[venediktov]

merged from asio branch , case closed !