Failing test case for sorting NaN values.
Better test case to demonstrate NaN sorting issue.

This also applies to undefined values, which is where I first noticed it
(a dataset where around half the values were undefined). This quicksort
implementation is unstable, so my previous attempt at an appropriate
test case didn't correctly detect the issue.
Fix sorting of undefined and NaN.

Unfortunately, this slows things down a bit due to the additional pass,
but perhaps it can be optimised later.
Simplify.
Fix insertion sort for NaN values.
added support for union of multiple filters
fixed bug - needed to expand hi0/lo0 range to include all ranges
Merge branch 'master' into union
Fix groupAll() after union reset.

This is also somewhat more efficient for large datasets, since it
recomputes group values from scratch rather than selecting all values,
removing them, and then adding them again.
Union of filters: return the dimension.

This is for consistency with non-union filters.
Add test for union of overlapping ranges.
Merging jasondavies/union
Merging jasondavies/sort-nan
Updating minified file