Fix mistakes in definition of CExecCallback

CExecCallback was not used by the higher-level interfaces, so this bug would
have only affected people using the FFI bindings.
No need for fromIntegral in 'bind', now that ParamIndex has an Int inside
Add lastInsertRowId, changes, and totalChanges

I deliberately did not export 'totalChanges' from Database.SQLite3,
to avoid confusion with 'changes'.
Improvements to Utf8 newtype wrapper

 * Add Ord and Monoid instances

 * Make Show instance correspond to IsString instance. Namely, don't show the
   Utf8 wrapper, and use Data.Text's show instance to render Unicode escapes
   instead of byte escapes.
Add execPrint, execWithCallback, and interruptibly
Merge pull request #22 from joeyadams/execPrint

Add execPrint, lastInsertRowId, and other improvements