Move documentation of config file from example config to man page.

[partim]

Currently, the available config options are documented through comments in an example config file. This makes the example config – which is also used as the default config by the packaging system – very long and confusing.

Instead, it would be better to have a config file section in the Krill manual page – or a separate manual page for krill.conf(5) – that contains all the config options and explanations for them.