HTTP file server

Initial implementation for serving static content from RxNetty based on https://github.com/netty/netty/blob/master/example/src/main/java/io/netty/example/http/file/HttpStaticFileServerHandler.java.  

Additional features include,
1.  Support for single and multiple file sources
2.  zero-copy serving of files

This isn't really accurate (and has a typo).  The LocalFile implementation doesn't check the the file is "found" or exists at all.  Short of a totally malformed string, not much in the way of sanity checks are promised.