Implement authorization header parsing

Basic HTTP authorization according to RFC 2617 is implemented.
Added an example of its usage with REST handler.

examples/basic_auth/README.md

@@ -0,0 +1,44 @@
+Cowboy Basic Authorization Rest Hello World.
+============================================
+
+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 run any given command or point your browser to the indicated URL.
+
+Examples
+--------
+
+### Get 401
+``` bash
+$ curl -i http://localhost:8080
+HTTP/1.1 401 Unauthorized
+connection: keep-alive
+server: Cowboy
+date: Sun, 20 Jan 2013 14:10:27 GMT
+content-length: 0
+www-authenticate: Restricted
+```
+
+### Get 200
+``` bash
+$ curl -i -u "Alladin:open sesame" http://localhost:8080
+HTTP/1.1 200 OK
+connection: keep-alive
+server: Cowboy
+date: Sun, 20 Jan 2013 14:11:12 GMT
+content-length: 16
+content-type: text/plain
+
+Hello, Alladin!
+```
+