Add some basic tests so Travis does more than just build.

These are some sanity tests to make sure we actually encode/decode things.

I'm using /usr/share/dict/words as a source of input.  If you're prefer
(because the line-endings suggest to me you're on windows) we can import a
novel from Project Gutenberg and use that instead so the data is actually
commited to the repo.

The snappy tests actually download their larger test data at benchmark time, if
requested, so that's an option too.  I wouldn't want to do that for the basic
tests though.