WIP commit
Update Slider to clip to range. Add slider transform class for working
with non-integer data.
BUG: when aligning one or zero items, silently return no constraints.
Merge pull request #236 from enthought/fix-align-one-item

BUG: when aligning one or zero items, silently return no constraints.
move the slider transforms to the Enaml stdlib
Set the slider bounds before the value to avoid inadvertent clipping.
Revert inadvertent changes to the example
Merge pull request #237 from enthought/feature-slider-update

Feature slider update