Rename project to playful

I'm finally getting around to releasing the project as a gem and came to realize that rubygems.org doesn't treat gem names as case-sensitive.  I was expecting to be able to release the gem under then "upnp" name, but since "UPnP" was already used, my push to rubygems.org failed.  Thus, I'm somewhat regretfully changing the name to "playful" (:-/).  I'll be releasing this as an rc.1 release, then adding more tests as my time allows, then doing the first "real" release.  Any help adding tests is completely welcome!