Made the debugger memory view not depend on isprint which is affected by
the global locale. Assume the OSD will display as ISO-8869-1 and
replace problematic printable characters.
Started changing Lua function bindings to use set_function to avoid
potential issues related to ThePhD/sol2#608, and worked out what was
causing problems with symbol table read_memory/write_memory. (They
aren't really essential - you can do the same thing with the address
space object itself, but they're easier to parameterise.)
394e5f18b6