v0.2.0.0

• Use a separate monad within withTransaction to prevent unsafe/arbitrary IO actions (#7, #28)
• Add MonadRerunnableIO to support IO actions within withTransaction only if the IO action is determined to be rerunnable
• Add built-in support for retrying transactions if a serialization error occurs
• Remove SqlQueryRep as an export from Database.Persist.Monad. You shouldn't ever need it for normal usage. It is now re-exported by Database.Persist.Monad.TestUtils, since most of the usage of SqlQueryRep is in mocking queries. If you need it otherwise, you can import it directly from Database.Persist.Monad.SqlQueryRep.