Export the psd in cms.SignedData

[tayler0101]

hi could please export the psd filed in
type SignedData struct { psd *protocol.SignedData }
or provide a function that return this filed

[btoews]

I think the intent was to keep the packages separate, but I can see how it would be useful to expose the *protocol.SignedData. I would accept a pull request changing the struct to

type SignedData struct {
  *protocol.SignedData
}

[ghaithsabba]

i created a pull request thanks in advance