Add function to retrieve recordings from database
Remove unused functions and add missing module exports.
Remove Connection type from Gramophone.Database

The purpose of the Connection type was to allow a reference
to an open database to be stored outside the model without
exposing the underlying database. Since the Database module no
longer exposes references to open databases (All exported
functions close the database before returning), the Connection
type was no longer necessary.
Add Haddock documentation for Database module.
Rename findArtist to findArtists

This makes the naming consistent with findRecordings and
findAlbums, and reflects the fact that the function return a
list.
Add addAlbum function to Gramophone.Database
Add addRecord function
Add type synonyms for database columns.

Fields in Album, Artist and Record types which had had generic
types (Text, Integer) now have descriptive type synonyms (Title,
TrackCount). Also changed NewAlbum, NewArtist and NewRecording
so they no longer use record syntax.