add 'hex' command to print a value in hex.
debug: implement proper skipping of subtrees for dwfLocal.

I made the dwarfEntry receivers mutable, which I don't think we
realy need anymore.  Maybe we'll make them taken by value again
later.

Also add some tests.
add way for dimensional to switch how the casting works.

just to see how it effects the assembly and whether we still work.
hook up symbolic execution stuff, get reading values working.

turned out the real issue was not accounting for the instruction
length when reading rip-relative addresses.  Anyway, now we do
things properly and can look up debug info.  Both gcc and clang
"dimensional" programs work with this commit.