Nuke server.py and the algorithm that it ran

Also fix up the testing client to instantiate Website
instead of Server
Nuke the execution module
Stop using aspen command in build system
Don't chdir() anymore

Calling chdir() was causing an issue serving the docs,
and had the potential to cause many more. Let's just Not Do That.
Manually chdir for docs

We stopped calling chdir automatically as part of our inversion effort
(we're a library, not a framework).
Rip out Socket.IO implementation

No two ways about it: if we're going to be "just a WSGI library" then we
can't implement Socket.IO ourselves. Instead we'll have to figure out
how to use gevent-socketio or similar. That rebuilding step is on the
other side of the Great Purge of 2014.
Watch the world burn.

This rips out network_address and network_engine and the rest of
sockets.W
Remove some more references to aspen executable

In docs and entrypoints.
Fix quickstart in docs to use `python -m aspen`
Remove NETWORK_ENGINES from __init__
Remove dead link to old aspen doc
Clean up Quick Start a little more
Merge branch 'master' into no_serverpy

Conflicts:
	aspen/__main__.py
	tests/test_sockets_transport.py
Merge pull request #324 from gittip/no_serverpy

No serverpy