Merge pull request #9 from dmcclean/master

Added clamp method for constraining a value to lie within an interval.
0.4.2 version bump and CHANGELOG
start split of standard interval arithmetic and Kaucher interval
arithmetic into separate modules
fix hull behavior on Empty
remove incorrect comment from back when we used 'rounded'
Added Numeric.Interval.NonEmpty. Wrote a simple 0.5 CHANGELOG
Ignore cabal sandbox.