Limit amount of type (d.ts) files exposed to users

[davidmrdavid]

After a discussion with @ejizba, we've learned that our TS project exports type-declaration files even for our internal utility files. This is problematic because it increases the type-management burden of our end users, and makes it inconvenient for us to import and reference external types in our project.

We should look to limit our exported *.d.ts files to include only public types.

[davidmrdavid]

FYI @hossam-nasr

[hossam-nasr]

Closed by #470