Allow to change the default configuration file to be loaded

[jdecool]

Hello,

I use Couscous in some of my projects but I don't the default configuration file couscous.yml to be mixed with my others files.

So I want to use another configuration filename, but currently it was impossible to change the configuration to be loaded.

Are you open to a PR that allow this change ?

I imagine something like couscous generate --configuration-file=, -f

[mnapoli]

Sounds great!