Simplify CharacterSet#initialize.

Significant portions of the code were duplicated.  This also addresses two
RuboCop warnings.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Remove useless return and self.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Switch one-line if blocks to guard clauses.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Use format instead of String#%.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Convert if ! into unless.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Remove useless variable assignment.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
spec: switch to single-quoted strings.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Use %w for multi-word arrays in specs.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
spec: use guard clauses where appropriate.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Mark ignored parameters.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>