v0.5.0

• #74: Accelerated set operations (union, intersection, difference,
  symmetric difference) by using larger blocks internally, by @james7132.
• #88: Added FixedBitSet::remove by @james7132.
• #89: Added FixedBitSet::zeros and the Zeros iterator by @james7132.
• #92: Added FixedBitSet::grow_and_insert function, a
  non-panicking version of insert that grows the underlying storage as need, by @shuoli84.
• #98: Ones now implements DoubleEndedIterator, by @tikhu.
• #99: Breaking change: serde now serializes and deserializes from a little-endian encoded
  raw byte buffer. Existing stored instances of the serialized bitsets will need to be
  re-encoded.
• Bumped MSRV to 1.56.