Pass remy.MODE_AUTODETECT to remy.init() instead of no parameters

Passing a named constant better communicates the intention that Remy
will perform autodetection. This is in preparation for an API change
that adds a parameter to remy.init().
Add Remy module for Lwan

This commit adds Remy module for the Lwan web server (http://lwan.ws).
Pass request parameter from request handler to Remy

In Lwan, handlers are defined like this:

	function handle_METHOD_NAME(req)
	   req:say('Hello, World!')
	end

Where METHOD is the HTTP method ("get", "post", etc), and name is the
canonical prefix for that particular URI (a "GET /" will have the
special NAME of "root", while "/foobar?param=3" will have "foobar" as
its name).

The `req` parameter is the only way one communicates with the request,
either to obtain some values (such as the query parameters) or to send
a response.
Improve Lwan detection by passing native_request to remy.detect()

Lwan detection is quite hackish at the moment (not unlike the other
ones, though), but it is good enough and still better than presuming
Remy is running under Lwan if all other modes fail for some reason.
Avoid autodetecting environment each and every request

This caches the result of remy.detect() inside the sailor table, and
reuses it next time remy.init() is called.  This works since the
`remy_mode` is `nil` the first time, which is a synonym for
`remy.MODE_AUTODETECT`; it is then assigned to whatever value defines
the current environment.
Merge pull request #30 from lpereira/lwan-support

Add preliminary Lwan support