[Feature Proposal]: Expose Package Manager's internal funcs as public

[bitwit]

First of all I just want to say thanks for the awesome project and, in particular, exposing the ScriptManager and PackageManager! I'm working on a project that is really benefitting from these being exposed.

I'm hoping to make a first contribution to this project by changing PackageManager's internal funcs to public because I'm interested in managing package dependencies in a way that would require using addPackage(at:) among others. I just wanted to inquire quickly first in case there was other justification for keeping them internal.

Second of all, if there are any related issues/bugs to Package Manager you need help with just let me know.

Thanks very much!

[orta]

Don't think so, I did this to a few of them recently also - #149