Befunge interpreter

A Befunge interpreter for challenge 164/hard.
Refactored Befunge interpreter

* Replaced the series of if statements on the instruction variable with
a lookup array containing function pointers.
* Moved the Befunge operator>> method from main.cc to Befunge.cc, where
it belongs logically.
* Improved error handling: actually print a helpful message and exit
gracefully instead of just throwing an exception.
Further Befunge refactoring

Replaced C-style array of function pointers with C++ array container of
std::function objects. Changed member variable naming style. Added two
sample Befunge programs.
Merge branch '164-hard'