python: Buffer input

Python doesn't have a function like C's getchar() to get a single
character of input, so buffer the input into a string instead.
python: Handle EOF errors when getting raw input
python: Dump interpreter memory in debug info
python: Step through program in debug mode
python: Strip off character from input buffer when reading
python: Count brackets instead of maintaining jump list

There was an issue before in which hitting a ']' would match the
wrong jump; this change should solve that (although rot13.bf still
fails to run).
python: Print debug information when memory pointer is invalid
python: Correctly jump

rot13.bf runs now, save for a minor issue in which you have to hit
"Return" to get the prompt back (will look into that issue).