#3 Add requirement for lz4 compression support

[Stefan Schlichting]

A CLIENT MAY indicate acceptance of a compressed TEXT SOAP ENVELOPE representation by including the Accept-Encoding header field into the HTTP-Header of a request MESSAGE where the list of encodings contains the value “x-lz4”.
NOTE—x-lz4 is proposed as the name for the content encoding in HTTP for content that was compressed using the lz4 algorithm in frame format [lz4ff].

If a CLIENT includes an Accept-Encoding header field in an HTTP-Header that contains the value “x-lz4” in a WS-Eventing [WS-Eventing] Subscription request, then the Event Source MAY transmit TEXT SOAP ENVELOPEs for events related to that subscription compressed using the lz4 algorithm in frame format [lz4ff].

A DEVICE SHALL include the Content-Encoding HTTP-field in a SOAP-over-HTTP MESSAGE with a value of “x-lz4”, if the TEXT SOAP ENVELOPE is compressed using the lz4 algorithm in frame format [lz4ff].

If a SERVICE needs to transfer a compressed TEXT SOAP ENVELOPE with UTF-8 character encoding, then it SHALL use the lz4 algorithm [lz4ff].

[lz4ff] https://github.com/lz4/lz4/blob/dev/doc/lz4_Frame_format.md

[Stefan Schlichting]

Clarify which method (gzip, zlib, exi, lz4) preferred?