Add `APIClient`, which is used to interact with the Freckle API
Add `APIClient`, which is used to interact with the Freckle API

* The `APIClient` class handles making calls to the Freckle API and
  parsing the responses, including handling pagination and setting the
  proper request paramters.
* Also creates special exceptions that explain what went wrong with an
  API call, and store the `errors` array for future use.

tcannonfodder/freckle-visualizer,tcannonfodder/freckle-visualizer