No default sections, when a config file is used.

[jcgruenhage]

Currently, there are some default sections. This is fine for people that just want a really basic changelog, but if people want something different, this might not work for them. Imagine someone doesn't want a bugfix list in his changelog, this is not something that is currently possible.

My proposal to fix this, is that if someone passes a config file in the arguments, or one is present in the current working directory, that no default sections are used, and instead only stuff out of that config file (and in the order it has in the config, like #102 suggests) is used.