GDB breakpoint like python's breakpoint

Launch ugdb and attach to current process with new tmux window.

``` rust use gdb_breakpoint::breakpoint;

pub fn main() { let x = 3 + 4; breakpoint(); } ```

Require nightly.

Recommendation

Multithreadding rust programs can call SIGSTOP many times. I recommend you to add following command into your .gdbinit file. So I used SIGINT instead of SIGSTOP on the second and later breakpoint calls.

handle SIGSTOP "nostop" "pass" "noprint"