Create node.http.Server and node.http.LowLevelServer

Create node.http.Server and node.http.LowLevelServer

The LowLevelServer is a direct interface to the parser given people access
to things like partially received headers. This could be used to implement
an extremely optimized server which acts before parsing is complete.

Most people will be using node.http.Server which is still rather low-level
compared to other http interfaces, but does take care of some details for
you.