Improve pastebin example

Reject more malicious paths.
Add a web server example

Explore re-routing in middleware.
Add EventSource example

Port from extend/cowboy_examples.
Merge branch 'pastebin_example' of git://github.com/acammack/cowboy
Merge branch 'web_server_example' of git://github.com/acammack/cowboy
Merge branch 'eventsource_example' of git://github.com/acammack/cowboy