Allow BitArrays

[nfoti]

It would be very useful to add support to pass BitArrays to map, reduce, and mapreduce (and the inplace versions). I'm not sure if this is as simple as adding it to the union of types that the arguments of those functions can be or if more significant changes need to be made.

Thanks.

[nfoti]

I took a shot at implementing this, but it was a bit more involved than I thought. A lot of the functions use ContiguousArrays, which BitArrays are not. I did get some code working for BitArrays, but the functions clobbered the ContiguousArray versions.