This change pulls as much pagination logic out of the database
implementation as possible. Database implementations should now be able
to marshal whatever state they need into opaque tokens with the
utilities in the pagination package.
This change refactors a lot of the code dealing with pagination so that
fernet implementation details do not leak.
- Deletes database/pgsql/token
- Introduces a pagination package
- Renames idPageNumber to Page and add a constructor and method.
This removes the `types` package instead moving the contents to the
top-level clair package.
This change also renames the `Priority` type to `Severity` in order to
reduce confusion.
This change also removes the IsValid method and replaces it with a safe
constructor to avoid the creation of invalid values.
Many docstrings were tweaked in the making of this commit.
