Move print_val() method out of tape class

I decided the tape shouldn't be responsible for printing. It seemed out
of scope. This change does result in a couple more lines of code, but I
believe it's worth it.
Reworked output of debug strings.

Debug strings will now all be output at the end of the event loop, and
it will always appear on its own line. This means that individual
characters output by the program will appear on their own lines, rather
than half way through a debug string.
Add support for input tapes.
Updated README.txt with new parameters and more implementation details