Change SignToolHelper syntax to reflect common call syntax

[pdfforge]

Until now, the call syntax of the SignToolHelper would have been
something like this:

 let signParams = {
     DevCertificate = cert
     Certificate = None
     FilesToSign = !! (buildDir @@ "**/*.exe")
     TimeStampUrl = None
 }

 Sign "packages/signtool" signParams

This does not go well with piping file sequences as it is used all
over FAKE. After this change, SignTool can be called like this:

 let signParams = {
     DevCertificate = cert
     Certificate = None
     TimeStampUrl = None
 }

 !! (buildDir @@ "**/*.exe")
   |> Sign "packages/signtool" signParams

From my point of view, this is more the "FAKE" way of doing things.

This is a breaking change though, as it changes the sytax of this helper and changes the SignParams type.

[forki]

yes this would have been better. But since it will break A LOT of builds I think it's not a good idea to change it.

[pdfforge]

Sorry for bothering again with this issue.

After some investigation, it happens that the file has never been in the build before (not even in the initial commit b21b39e). So in my opinion, this can safely be merged, as it had not been included.

If you don't agree, that's ok of course ;-)