Stop using void* in a bit_vector's constructor.
Stop using void* in a bit_vector's constructor.
Modify a constructor which receive external memory to copy to its own memory from the external memory.
Remove an unnecessary constructor.

The removed one is same as its const version.
Remove an unnecessary const_cast.
Make driver_base noncopyable
Merge pull request #33 from gwtnb/bit_vector

Make bit_vector safer.
Merge pull request #36 from gintenlabo/make-drivers-noncopyable

Make driver_base noncopyable