Overhaul ROP.setRegisters to support more complex cases needed by AMD…

…64 (#1044)

* Overhaul ROP.setRegisters to support more complex cases needed by AMD64

Additionally, have a separate cache for ROPs composed of multiple ELF files

* Better presentation for stack padding slots

* Remove unnecessary stack adjustment on amd64

For amd64, it is possible that len(stackArguments) == 0.

* Add a doctest for amd64 register dependency stuff

* More i386 adjust optimizations

* Use nextGadgetAddr as the adjust value

* Always use padding for the last "ret" adjustment

* Better dump display

* Update doctests for new ROP dump() enhancements

* Add badchars support for ROP gadgets

* More doctest fixes, also ensure ROP.search does not return gadgets ending in e.g. int 0x80