Merge branch 'master' of github.com:rupa/z

version 1.8 PROMPT_COMMAND, cleanup

version 1.7 x and c options, prompt cmd append, revert exec warning

version 1.6 subdirs, option combining

version 1. exclude dirs

version 1.4 zsh changes (breaks backward compatibility)

version 1.3 tab completion improvements

version 1.2

version 1.1

Just a release for those who prefer not to track HEAD