Illustrate the use of min and max

Adding test which shows how min and max constrain the duration of an animation.

(max=indefinite has no effect, as does min=0.)

min and max are specified at
http://www.w3.org/TR/SMIL3/smil-timing.html#Timing-MinMax

This new test can be viewed at
https://rawgit.com/ewilligers/svg-animation/min-max/examples/compare.html?name=min-max