Add optional automatic response body compression

This behavior can be enabled with the `compress` protocol option.
See the `compress_response` example for more details.

All tests are now ran with and without compression for both HTTP
and HTTPS.

examples/compress_response/README.md

@@ -0,0 +1,62 @@
+Cowboy Compress Response
+========================
+
+To compile this example you need rebar in your PATH.
+
+Type the following command:
+```
+$ rebar get-deps compile
+```
+
+You can then start the Erlang node with the following command:
+```
+./start.sh
+```
+
+Then point your browser to the indicated URL.
+
+Example
+-------
+
+``` bash
+$ curl -i http://localhost:8080
+HTTP/1.1 200 OK
+connection: keep-alive
+server: Cowboy
+date: Mon, 07 Jan 2013 18:42:29 GMT
+content-length: 909
+
+A cowboy is an animal herder who tends cattle on ranches in North America,
+traditionally on horseback, and often performs a multitude of other ranch-
+related tasks. The historic American cowboy of the late 19th century arose
+from the vaquero traditions of northern Mexico and became a figure of special
+significance and legend. A subtype, called a wrangler, specifically tends the
+horses used to work cattle. In addition to ranch work, some cowboys work for
+or participate in rodeos. Cowgirls, first defined as such in the late 19th
+century, had a less-well documented historical role, but in the modern world
+have established the ability to work at virtually identical tasks and obtained
+considerable respect for their achievements. There are also cattle handlers
+in many other parts of the world, particularly South America and Australia,
+who perform work similar to the cowboy in their respective nations.
+
+$ curl -i --compressed http://localhost:8080
+HTTP/1.1 200 OK
+connection: keep-alive
+server: Cowboy
+date: Mon, 07 Jan 2013 18:42:30 GMT
+content-encoding: gzip
+content-length: 510
+
+A cowboy is an animal herder who tends cattle on ranches in North America,
+traditionally on horseback, and often performs a multitude of other ranch-
+related tasks. The historic American cowboy of the late 19th century arose
+from the vaquero traditions of northern Mexico and became a figure of special
+significance and legend. A subtype, called a wrangler, specifically tends the
+horses used to work cattle. In addition to ranch work, some cowboys work for
+or participate in rodeos. Cowgirls, first defined as such in the late 19th
+century, had a less-well documented historical role, but in the modern world
+have established the ability to work at virtually identical tasks and obtained
+considerable respect for their achievements. There are also cattle handlers
+in many other parts of the world, particularly South America and Australia,
+who perform work similar to the cowboy in their respective nations.
+```