RFR JDK-8153353: HPACK implementation

[Pavel Rappo]

Hi,

Could you please review my change for JDK-8153353?

http://cr.openjdk.java.net/~prappo/8153353/webrev.00/

This is an implementation of HPACK (Header Compression for HTTP/2) [1]
Internal API classes are (package sun.net.httpclient.hpack):

    Encoder, Decoder and DecodingCallback

Example of their usage can be seen in the RFR for HTTP/2 implementation
published previously today [2, 3].

Thanks,
-Pavel

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[1] https://tools.ietf.org/html/rfc7541
[2] http://cr.openjdk.java.net/~michaelm/8087124/webrev.1/src/java.httpclient/share/classes/java/net/http/Http2Connection.java.html 304:306
[3] http://cr.openjdk.java.net/~michaelm/8087124/webrev.1/src/java.httpclient/share/classes/java/net/http/Http2Connection.java.html 682:695