Small clean up in loop filter code

mentioned in issue #15 (closed)

mentioned in issue #61 (closed)

mentioned in issue #62 (closed)

mentioned in issue #63 (closed)

mentioned in issue #64 (closed)

mentioned in issue #65 (closed)

mentioned in issue #66 (closed)

mentioned in issue #67 (closed)

mentioned in issue #68 (closed)

mentioned in issue #69 (closed)

mentioned in issue #70 (closed)