custom exception classes inherit from StandardError instead of Exception

It's useful to be able to rescue all exceptions thrown by this API for a few reasons.  First, it's the simplest way to implement the integration.  Second, it's not initially obvious to the developer which exceptions will be thrown in which situations.  Third, there's always the possibility of a bug in the library, the API, or the service itself.

It's not a good idea to rescue Exception because there are subclasses of that class that should not be rescued in the context of control flow logic.
http://stackoverflow.com/questions/10048173/why-is-it-bad-style-to-rescue-exception-e-in-ruby

Altering these classes so that they inherit from StandardError instead has no consequences and is the intended way for Ruby exception classes to be written.