write support for PE / Signing PE for UEFI

[baloo]

As part of signing PE objects for booting UEFI payloads with secureboot, we (@RaitoBezarius and I) would need to add a PKCS#7 signature to PE objects.

This comes along with the efforts @RaitoBezarius already submitted in #354 and the request for authenticode support in #355.

@m4b I'd love for your opinion on that, and input on where to direct efforts.
Should we target https://github.com/m4b/faerie for write support, or should put PE write support in goblin?

[m4b]

Usually the first step is to add Pwrite methods to the various PE structs, ideally deriving them (as I see your WIP PR appears to?). Then if you wanted, you could add support for writing out pe object files in faerie

[RaitoBezarius]

@m4b Awesome, how do you want me to develop this PR? Should I split in atomic PRs or should I make a big PR? What do you prefer?