Handle arrays with null elements

[carpiediem]

It would be great if the library included a configuration parameter that would let users define how null values should be handled. There ought to be three options:

1. Any null values should trigger a failed assertion (current behavior)
2. Expect all null elements to be placed before -∞ (depending on sort order)
3. Expect all null elements to be placed after +∞ (depending on sort order)

Maybe something like this?

expect(["b","apples",null]).to.be.sorted({descending: true, null:"low"});  // TRUE
expect(["b","apples",null]).to.be.sorted({descending: true, null:"high"});  // FALSE
expect(["b","apples",null]).to.be.sorted({descending: true, null:"none"});  // FALSE

[carpiediem]

After testing some more, it looks like #2 is the current behavior (which is the probably the best default). Still, it would be nice to have the configuration option.