libdeflate as inflation ("decompression") fast path

Resurrecting support of libdeflate, now specifically only for inflation and only as a fast path to zlib.

WITH_LIBDEFLATE=1 make

builds examples using this fast path (you need to build the submodule first). Improved load_test.c benchmark can now highlight inflation cost:

For me and my particular test system:

• With dynamically linked zlib - 110k msg/sec inflated and echoed 300 byte JSON messages
• With statically linked zlib-cloudflare - 130k
• With libdeflate as fast path - 180k
• Without any inflation - 320k

Note: WITH_DEFLATE is only compatible with uWS::SHARED_DECOMPRESSOR!