debug eval readline loop with reflection and upvals

[rurban]

the current debug eval readline loop (IN_C and in .pn) doesn't allow access to registers, locals, upvals and values (paths) as :r,:l,:v,:u.

remote debuggers need the functionality as spec'd in https://github.com/perl11/potion/wiki/Debuger-interface

:debug (global debug object, bound to the debug object, prefixed with :)
:ast (current ast)
:cl (current closure)

debug getinfo = (level, name): .
debug getlocal = (f, i): .
debug setlocal = (f, i, name): .
debug setupvalue = (f, i, name): .
debug traceback = (f| level): .

We need to do this in a new closure with those values locally defined.