v6.0.1

CHANGES:

breaking changes

• Cstruct.len is deprecated, it will be deleted at the next
  release. You should use Cstruct.length instead.
  (@dinosaure, @hannesm, #284)

• Remove color from ppx's binary to replicate diff of errors in
  any contexts (@dinosaure, @sternenseemann, #285)

• Add shiftv (@talex5, @avsm, @dinosaure, #287)

• Use Bytes_val if available (@hannesm, @avsm, @dinosaure, #286)