Use cbitset crate instead of custom bitset implementation in select

Removed custom bitset implementation from select according to #151 (closed).

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.