Use cbitset crate instead of custom bitset implementation in select

Removed custom bitset implementation from select according to #151.

Something I'm not sure about is that, by looking at its source code, cbitset seems to provide BitArrays of lengths up to 16 and since unsigned long can have 4 bytes it's possible the bitset used here would exceed that limit. I am able to create a BitSet with length greater than 16 on my machine which is why I haven't changed it to c_ulonglong and instead provided this information.

I also changed a weak inequality to a strict one as I believe it was incorrect.