2.0.0

Added

• Interface Encoder EncodeSortable() ([]byte, error). It allows you to
  define the sortable encoding of your own types.
• Add godoc example of Encode() with output.
• Add encoding for []byte by returning copy of slice.

Changed

• BREAKING Encode() no longer guarantees len(x) > 0.
  Up to this point it was only relevant for strings. Empty strings used to be
  encoded as 0x00 to avoid empty slices for direct use as Bolt keys. Now an
  empty string is encoded as an empty byte slice.
• Improve speed by 30% on average by inlining code. See commit ab2cdb7 for
  details.