Added Dominik's code.
Adpated hybrid_vector

* fixed initialization bug in hybrid_vector (set m_size to 0)
* added naive implementation of get_int (should be done more efficient)
* added hybrid_vector to tests
raw uint8_t array -> int_vector<8>
Added rank0 implementation
 __builtin_popcountll -> bits::cnt
Added copyright again.
Renaming hybrid_bitvector to hyb_bitvector.
Merge pull request #205 from simongog/hybrid_bitvector

Added hybrid bitvector