Issue 31

I can make the argument against having `CacheWriterException` being thrown from the writer using any `RuntimeException` instead of `SQLException`... but that being said, declaring all methods on `CacheWriter` to throw `Exception` and wrap these in `CacheWriterException` does make sense sense to me right now, and seems true to the general spirit of exceptions in the code so far... 
Anybody thinking that's a stupid idea?