Remove develop_server.sh in favour of pelican serving static files itself

Competing static site generators integrate the functionality of regenerating
content and serving it into their main executable. In pelican this
functionality used to be in an external script `develop_server.sh` which
resides in the blog base directory. This has the disadvantage that changes in
pelican can break the `develop_server.sh` scripts which will not automatically
be upgraded together with pelican by package managers. Thus, pelican should
integrate this functionality into its main executable.

To this end, this commit removes `develop_server.sh` and adds three command
line options to the pelican executable:

 * `-l/--listen` starts the HTTP server (`-s/--serve` was already taken)
 * `-p/--port` specifies the port to listen at
 * `-b/--bind` specifies the IP to bind to

`--listen` and `--autoreload` can be used together to achieve the same
effect that other static site generators offer: Serve files via HTTP
while at the same time auto-generating the content.

Since the `develop_server.sh` script was removed, pelican-quickstart looses the
`develop` option.

Since the `develop_server.sh` script was removed, the Makefile looses the
`stopserver` target and the `devserver` target is replaced by running `pelican
-l` in the foreground.

Since pelican now offers the `--listen` option, the fabfile uses that instead
of starting the socketserver itself.

docs/quickstart.rst

@@ -61,11 +61,10 @@ ignored for now.)
 Preview your site
 -----------------
 
-Open a new terminal session and run the following commands to switch to your
-``output`` directory and launch Pelican's web server::
+Open a new terminal session, navigate to your site directory and run the
+following command to launch Pelican's web server::
 
-    cd ~/projects/yoursite/output
-    python -m pelican.server
+    pelican --listen
 
 Preview your site by navigating to http://localhost:8000/ in your browser.