Parametrize output files.

[sholsapp]

Nearly all of the output files generated are specific to https://github.com/sholsapp/gallocy. Before cthulhu is actually usable in other contexts, this has to be fixed.

This can be fixed by adding a configuration file that specifies an input template to each function that generates an output file. Whatever markup language we use in the configuration file, it should be easy to support multiline entries (after all, we'll be specifying bash scripts, code snippets, and more in this file).