adding configuration option to use different migrations directory

[skecskes]

Hi,

I had lately issue with migrations, because the config file and migrations file are in different folders. I couldn't use even current working directory because that broke paths in configuration file require statements. The only solution for me seems to have special parameter to define migrations folder separately, same as config file is defined separately. Please, can you accept this merge request and then update the npm too?

Btw, thanks a lot for repo. It saves me lot of time. :)