Fix BitVector set/clear range functions

Fix off by one errors in de.polygonal.ds.BitVector .clrRange/.setRange.
Also add new tests for setting and clearing ranges on a bitvector.
Optimize BitVector.clone

Use Vector.blit to copy the bits. This should result in a speedup on some platforms, by using smart memory copying.
Fix BitVector.resize

Make BitVector follow its stated api:
Even when number of bins stay the same, if the new size smaller, clear bits. if new size is bigger, keep old bits.
Merge pull request #14 from Dr-Emann/Fix_BitVector

Fix bit vector