Add support for decompressing gzip or raw deflate

[mstange]

Using fdeflate to decompress gzip is somewhat tricky at the moment, because fdeflate expects a zlib header and a zlib trailer. For the trailer, you can ask it to ignore the checksum, but it still consumes a few bytes of the trailer and the caller doesn't know where the deflate stream ended (and where it needs to look for the gzip trailer).

[fintelia]

Adding deflate handling seems reasonable and shouldn't be a big change. Supporting the rest of gzip would probably be more involved