ErrDuplicateEmail adds a new ErrDuplicateEmail error.

ErrInvalidCredentials adds a new ErrInvalidCredentials error.

ErrNoRecord adds a new ErrNoRecord error.

Define a Snippet type to hold the data for an individual snippet.

Define a SnippetModel type which wraps a sql.DB connection pool.

Define a new UserModel struct which wraps a database connection pool.