Use public api, move functions into public api

@forki I worked a bit on https://github.com/fsprojects/Paket/issues/341 - please offer guidance and I can continue if you like the direction. 

Thanks, 

Brody 

Need review on:

* Should these be public APIs?
* What should be done with bool flags?
hmm I don't get it, are we ignoring all arguments now? how about when the dependencies file is missing ?