Constructor taking ownership of a `Vec<u8>`?

[joshtriplett]

If I have a Vec<u8> that I want to turn into a BitVec, currently I need to call from_bytes, which copies the bytes. I'd love to have a from_vec (or an impl From<Vec<u8>> for BitVec) that takes ownership of the Vec, so it doesn't need to copy.

[pczarn]

This would have us re-interpret the Vec<u8> as Vec<u32> (or potentially also Vec<B> such as Vec<u128>) which is not that simple

[pczarn]

If we do this, then also the inverse (into_bytes) similar to #127

[pczarn]

@joshtriplett I will do this for 0.10.0