bfi: brainfu** interpreter in x86_64 because it is possible

about:
	this is a little practice on interpreters, i chose brainfuck since it has
	a small instruction set and since i am using x86_64 i thought it'd be cool (it was)

run:
	$ docker build bfi .
	$ docker run -it bfi:latest sh
	# make
	# ./bfi <program>

why using docker:
	why not? but the real answer is: the interpreter depends on tiny-pf and xvargs,
	both are different projects and the most important one, i did not want to have
	brainfuck files in the original repo