Add an option to load a file containing redirects (source, target paths)
and serve them from the HTTP server, to allow renaming a radio without
breaking old links.

This change involves a refactoring of the DNS redirector code, which is
now a bit cleaner and has proper tests.

- Changed package name to autoradio-server to avoid conflicts;
- fixed systemd service files and defaults;
- added sudo configuration to restart icecast2;
- removed obsolete prerm/postrm scripts.

It should work with Debian wheezy (sysvinit) and jessie (systemd)
without having to pass a reload command as a command-line flag.

Enabled by setting the --debug-addr command-line option.

This provides some discovery capabilities to radiod and redirectord, so
that in most cases fewer command-line options are required for operation.

Split networking is where nodes communicate among themselves on a
private network (for example when behind a NAT infrastructure). This
change adds the --internal-ip option to radiod, that advertises a
separate IP for internal communication.

The only thing we need from ghost is the GZIPHandler. The
gorilla/handlers package has a CompressHandler, and much fewer
dependencies. Also, add a test that attempts a request with
an Accept-Encoding: deflate header.

RemoteAddr again.

Also removed some unnecessary duplication of code from net/http.