WIP add recipe for reloader

@zzak asked for a Rack::Reloader recipe in #44 

this isn't that, but:
1) it's worthwhile to have this alongside the shotgun recipe, since that doesn't work for Windows.
2) what's the motivation behind a rack::reloader recipe, exactly?

this is a bit of a rewrite of http://www.sinatrarb.com/contrib/reloader.html which i think is a lil confusing (don't weave classic + modular app implementations, just present each individually, IMO)

i'm also going to write up a recipe for rerun. do we think that reloader, shotgun, and rerun should all be one article on reloaders? 3 makes a category, right, heh?