Hack to allow the vim-tmux-navigator plugin key bindings to interupt.

I'm sure there is a more elegant and flexible solution available, but thought it worth mentioning that I have just created this hack to work around #166 for myself.

This allows the <c-h>, <c-j>, <c-k> and <c-l> binding provided by the
vim-tmux-navigator plugin to be used to switch to a tmux pane while
vdebug waits for a connection to the debugger.

This is useful when debugging cli scripts and you need to change to a
differnt tmux pane so as to execute your script.