Upgrade to httpclient 5

Notable changes and features included in the 5.0 series are:

    Support for the HTTP/2 protocol and conformance to requirements and recommendations of the latest HTTP/2 protocol specification documents (RFC 7540, RFC 7541.)

    Supported features:
        HPACK header compression
        Stream multiplexing (client and server)
        Flow control
        Response push
        Message trailers
        Expect-continue handshake
        Connection validation (ping)
        Application-layer protocol negotiation (ALPN)
        TLS 1.2 security features
    Improved conformance to requirements and recommendations of the latest HTTP/1.1 protocol specification documents (RFC 7230, RFC 7231.)
    New connection pool implementation with lax connection limit guarantees and better performance under higher concurrency due to absence of a global pool lock.
    Support for Reactive Streams API [http://www.reactive-streams.org/]
    Package name space changed to 'org.apache.hc.client5'.
    Maven group id changed to 'org.apache.httpcomponents.client5'.

    HttpClient 5.0 releases can be co-located with earlier major versions on the same classpath due to the change in package names and Maven module coordinates.

Notable changes and features included in the 5.0 series:

    Support for HTTP/2 protocol and conformance to requirements and recommendations of the latest HTTP/2 protocol specification (RFC 7540, RFC 7541)

    Supported features:
        HPACK header compression
        stream multiplexing (client and server)
        flow control
        response push (client and server)
        message trailers
        expect-continue handshake
        connection validation (ping)
        application-layer protocol negotiation (ALPN) on Java 9+
        TLS 1.2 security features

    Features out of scope for 5.0 release:
        padding of outgoing frames
        stream priority
        plain connection HTTP/1.1 upgrade
        CONNECT method
    Improved conformance to requirements and recommendations of the latest HTTP/1.1 protocol specification (RFC 7230, RFC 7231)
    New asynchronous HTTP transport APIs consistent for both HTTP/1.1 and HTTP/2 transport.
    Redesigned I/O reactor APIs and improved NIO based reactor implementation for a greater performance and scalability.
    Support for server-side request filters for classic and asynchronous server implementations. Request filters could be used to implement cross-cutting protocol aspects such as the 'expect-continue' handshaking and user authentication / authorization.
    Support for Reactive Streams API [http://www.reactive-streams.org/]
    Redesigned connection pool implementation with strict connection limit guarantees. The connection pool is expected to have a better performance under higher concurrency due to reduced global pool lock contention.
    New connection pool implementation with lax connection limit guarantees and better performance under higher concurrency due to absence of a global pool lock.
    Package name space changed to 'org.apache.hc.core5'
    Maven group id changed to 'org.apache.httpcomponents.core5'