Support FromCtx and IntoCtx for pe structs

[Ben-Lichtman]

the layout of PE structs is pretty well documented, so it should be possible to turn PEs to and from bytes.

If this is not completely possible, it should at least be mostly possible - however many of the headers don't implement the correct traits.

[m4b]

So I thought the PE structs implemented FromCtx (reading) ? However for I don't think IntoCtx has been implemented yet (writing)

That would be pretty awesome :) I think the only reason it isn't done is simply no one had the time to write the corresponding IntoCtx trait impls (e.g., like was done for mach + elf); if you'd like to send a PR, that would be great!