bfstk, a brainfuck~ish interpreter

Implementation notes:

• the data pointer starts on cell zero; and
• cells extend (virtually) unlimited to both the negative and positive directions.

To run:

cargo run -- examples/hello_world.b

or compile first, then run:

cargo build --release
./target/release/bfstk examples/hello_word.b

Run with -r to show a summary report of the state after execution.

Run with -d to dump the left (negative space) and right (positive space) memory blocks after execution.