added breakpoint option

[rewk]

Hi !

I've been using your great emulator for a few days now. But I was missing a way to easily add a breakpoint and run the program from the autoexec.txt.

That's why i've added the -b --breakpoint option. It also was easier for me to debug with a zero initialized memory, hence, the -z --zero option.

What do you think about it?

(And also it's my first ever pull request on github...)

[rewk]

I used the wrong user in my commits. I will do this again.