XPWS Daemonize

This pull request adds Un*x daemon control features to `xpws`:

```sh
$ xpws start
[xpws-dev#3724] running localhost:8080 @ C:\cygwin\home\friebe\devel\rest-file-upload - Use xpws stop to end

$ curl http://localhost:8080/
[ { "name" : "class.pth" , "mime" : "application\/octet-stream" , "size" : 14 , "modified" : "2013-11-01T11:42:31+01:00" } , { "name" : "data.xml" , "mime" : "text\/xml" , "size" : 117 , "modified" : "2013-10-21T20:25:33+02:00" } , { "name" : "innovate-or-die.png" , "mime" : "image\/png" , "size" : 68763 , "modified" : "2013-10-21T20:23:59+02:00" } ]

$ xpws status
[xpws-dev#3724] running C:\Users\friebe\AppData\Local\.xpws.pid

$ xpws stop
[xpws-dev#3724] shutting down...
```