add spec for chunked response with "Connection: close" header.
add spec for chunked response with pipelined request.
handle connection state properly when the response is chunked.
combined chunked response specs.
reset request state when response state is set to the initial state.
Support verification of client-side SSL certs

Added an explicit option for SSL's `verify_mode`. In the event that a CA file
or CA path are passed, default to expecting clients to have signed certs. If
nothing is provided, use the preexisting behavior of not verifying clients.
Test with signed client certificates
Test with signed server certs, too
Test for failure with unsigned client certificates
Allow for serving HTTP over UNIX sockets
Update comments to reflect more generic communication channels
Merge pull request #115 from stouset/http-over-unix-sockets

Allow for serving HTTP over UNIX sockets
Merge pull request #113 from stouset/client-ssl-certificates

Client SSL Certificates
Fix Reel::Server::unix

The ::unix method tried called `super`, which fails (it had intended
this to be delegated to the superclass' `new` method. We alias `new` so
that it can be called by all existing factories for the time being.

After speaking with Tony, the plan is to potentially remove this change
later, relying entirely on subclasses. This might involve a breaking API
change, however, so this approach is minimal-touch for the time being.
Added tests for serving HTTP over UNIX sockets
Merge pull request #116 from stouset/http-over-unix-sockets

Fix Reel::Server::unix
Merge pull request #112 from unakatsuo/fix-chunked-with-connclose

Socket closed unexpectedly for chunked response with "Connection: close" request
Prevent nil current_request

Seeing a lot of:

```
NoMethodError: undefined method `handle_response' for nil:NilClass
```

So catching that scenario.
Remove duplicated comment.
Add SocketMixin for de/optimization per-server.