Introduction of the support of RAW lines.

Introduction of the support of RAW lines.

This patch fixes https://github.com/StevenBlack/hosts/issues/1563#issuecomment-810688754

Indeed, before this patch, the updater was not supporting a RAW (not
hosts) list of domains as input.

Changes:

    matches_exclusions():
        (new) Support for rule formatted as 'example.com' along with
              the pre-existing '0.0.0.0 example.com'.

    normalize_rule():
        (edit) Apply DRY.

        (new) Support the normalization of the rule formatted as
              'example.com' along with the pre-existing '0.0.0.0
              example.com'.

    strip_rule():
        (new) Complete rewrite in order to strip all possible lines.