Add support for deflate compression.

I added support for the deflate encoding type in the event that gzip isn't supported by a client.

questions:

1. Do you want to support deflate?
2. The deflate encoding level is set to `-1`, the default value. The higher the value (up to 9), the better the compression, but the worse the performance. If you want to add deflate, do you have an idea what level you would like to set?