Default Accept-Encoding header for the client

[Yogurt4]

Suggestion: httplib::Client could set a default Accept-Encoding header automatically, based on the compile options, like

#if defined CPPHTTPLIB_ZLIB_SUPPORT
		{ "Accept-Encoding", "gzip, deflate" }
#endif

(plus the combinations with Brotli).

It's quite trivial to implement. Shall I provide a pull request though?

[yhirose]

@Yogurt4 I implemented it. Thanks for the suggestion!

[Yogurt4]

Wow! Thanks for the superfast response, and for implenting it.