Fix class documentation of CircleFlowIndicator

In HTML, a list item should be enclosed in <li>, not <ul>,
which is for the whole list.
Add snap option to CircleFlowIndicator

like ViewPagerIndicator's. It makes the active indicator jump to the
next position instead of following the scroll offsets. I've also
documentated it in the README.
Make flings smoother by starting at the drag speed

Previously, flinging felt a bit jerky, because if you were moving fast
when you released your finger, it would immediately switch to its
preferred snapToScreen speed. Now, it uses the velocity you had at
release, to make it feel more like it's responding to your control. It
looks a lot smoother now.

I feel like it ought to decelerate over the course of the fling rather
than stopping abruptly at the next page, but the new behaviour is the
same thing that ViewPager does.
Further work to onMeasure

to support the interior views being wrap_content.
Merge branch 'measure'