Support keyTimes and keyPoints in Motion path

keyTimes is mentioned in
http://www.w3.org/TR/SVG/animate.html#KeyPointsAttribute
and defined in
http://www.w3.org/TR/SVG/animate.html#KeyTimesAttribute

keyPoints is defined in
http://www.w3.org/TR/SVG/animate.html#KeyPointsAttribute
Merge pull request #85 from ewilligers/fast-motion-path-pacing

Support keyTimes and keyPoints in Motion path