Add -static and -serve options.

-static provides a custom path for the static files which form the
notebook.  It can be used to serve iocamljs, for example;

```
iocamlserver.byte -static /home/andyman/.ipython/profile_iocamljs
```

This is pretty close to the profile option of ipython.

-serve <uri> <path> enables serving of files from the filesystem.
This is specifically used by iocamljs to read files using
XmlHttpRequest.  For example;

```
iocamlserver.byte [...] -server mybuild _build
```

```ocaml
let xml = XmlHttpRequest.create ()
let () = xml##_open(Js.string "GET", Js.string "file/mybuild/_log",
Js._false)
let () = xml##send(Js.null)
let r =
    if xml##status = 200 then
        Js.to_string (xml##responseText)
    else
        "BAD"
```

Note that we internally require the `file/` prefix in the uri to
distinguish between other uris.  In this case `file/mybuild/_log` is
mapped to `_build/_log`.

Next step is to see if this can be used with the psuedo file system.  If
that works we'll try loading a cmo file.