Import cleanup, warning fixes, typo fix, bump version bounds

These changes achieve the following:

* Bump the upper version bounds of several required packages, including `lens` and `attoparsec` (which fixes issue #3). I also lowered the min bound of `transformers` to 0.3, since GHC 7.8.3 is built against that version.
* I went through the source files reorganizing imports and fixing compiler warnings, just to be tidy. There are still a few warnings in `tests/Core.hs` that I did not fix since it would require adding new implementation (e.g., additional pattern matches for `instance Show row => Show (CRUDAction row a)`.
* I fixed a typo by changing the `persistantCRUD` function to `persistentCRUD`. I'll let you decide if that warrants bumping the version number.