zsh: support more variants of `jump` targets
zsh: support more variants of `jump` targets

Given a hash like "modules" that maps to some directory, now you can
jump to a subdirectory with either of these:

  j modules/apps
  j ~modules/apps

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent