Nicer plotting graphs of function interval approximations - blur
boundaries are darker than the inner approximation.
Some instances for Bool and Maybe and ().
Added refinement order instance for IntevalApprox.
Function to test inclusion of two intervals approximated by
IntervalApprox.
Made Nothing the largest element of a Maybe type so that this type can
be used as a measure of *imprecision*.
Union of interval approximations.
small improvements in demos