This adds a configuration section to config.yaml which allows users
to enable/disable each fetcher at runtime.
Signed-off-by: Avi Miller <avi.miller@oracle.com>
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.
