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 doesn't work.  It seems like the write does need to be flushed after all.