We now do not allocate memory for headers and other metadata unless
requested by the caller. Instead, we read-in the entire contents
of the image into memory and operate on pointers and casts wherever
possible. I have a left a TODO to hook up Windows' memory-mapped API
here in-place of standard `readToEndAlloc` which should be more memory
proof on memory constrained hosts.
This commit also supplements our `std.coff` with a lot missing basic
extern structs required to make our COFF linker.
c84e5ee878