It varies between systems if /usr/bin/python is Python 2.x or Python
3.x. Since we now only work with Python 3.x we should be more explicit
in our scripts and documentation.

* Use double quotes around `"$@"` to fix invocation with arguments
  including spaces.
* Use double quotes around `"$(dirname "$0")"` to fix invocation
  inside a directory path including spaces.
* Use `set -e` to abort in case `cd` fails.
* Use `exec` to avoid forking an unnecessary wrapper process.
* Skip an unnecessary `cd` → `pwd` → `cd` dance, just use `cd`.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

realpath isn't available on older systems, so use a safer approach
using just very basic commands.

We should only start the server if we are the main module, and not
imported some other way. This is important for multiprocessing to
work correctly on Windows.

Signed-off-by: Rohan Jain <crodjer@gmail.com>

Make websockify subdirectory and move websocket.py ->
websockify/websocket.py and websockify ->
websockify/websocketproxy.py. Create a ./run script that launches
websockify as before (unfortunately can't have a websockify script at
the same level since this is now a directory). Make websockify.py
a symlink to ./run. Once the package is installed, the main launch
script will be /usr/bin/websockify.

This makes it easier to package up websockify as a python module.
setup.py should now properly install websockify as a module.

Note that to include the base websocket module/class you will now do:

    import websockify.websocket
    #OR
    from websockify.websocket import WebSocketServer

To import the full websocket proxy functionality:

    import websockify.websocketproxy
    #OR
    from websockify.websocket import WebSocketProxy

This will also help with startup speed slightly because the code in
websocketproxy will now be byte compiled since it is no longer in the
main invocation script.