Ghc api

Added an implementation for addItemsToImport, which reuses much of the code for addHiding. I reused it by extracting a new helper function called addItemsToImport'. In addition to addHiding's signature, addItemsToImport' receives an argument for the type of operation.

The only difference from the current addItemsToImport to the one in the old API is the lack of a conditional identifier. I plan on adding it soon, but decided to commit like this for the night.

In addition, I have already merged everything with your branch. I didn't have to solve any conflicts. All tests that passed on travis are passing on my build environment.

PS: I realized after pushing that some of my commit messages started to show grammatical errors. I apologize: as it gets late, my ability to form correct phrases decreases.